Since you were poking around the front of the engine. Try disconnecting your MAF sensor (this is the one that goes on the air intake infront of the throttle. What happens is the truck starts and the computer tries to use the sensors to control the idle / mixture and either the MAF isn't working or there is a leak of air behind it (air getting into the engine that is not being measured). So the computer thinks no air is getting into the engine and as a results cuts the fuel (fuel and air must enter at a pretty well control ratio - no air means no fuel or rather, no measured air... no fuel). By disconnecting the sensor, you are telling the computer something is wrong and computer goes into a computation mode were it computes how much air in thinks got into the engine and you will run. It will set the check engine light but its actually amazing how well it runs (for those that are interested its called "speed density" mode). If that fixes the problem, examine all the rubber hoses fitting etc. and make sure...

If you do a full computer scan of that truck it should include ABS. My tool will tell me if the ABS computer is not responding (on my 2007). Heck the scan tool checks computers in my seats, stereo, nav etc. etc. Some dealerships will also scan for free. I know some repair shops that will as well. BTW, when you replace the master cylinder, did you do a full ABS bleed? On my '07, there is a special bleeding procedure that gets the air bubbles out of the ABS unit. That requires a scan tool that can do "special tests". Auto Enginuity is the one I used. I don't think my old OTC scanner will even do it (even though it covers up to 2014 or so).

Coil box? Ignition coils? On the hemi head, there is a seal around the coils that is supposed to keep the oil under the valve cover. When that fails, you get oil around the spark plug etc. - real mess. The fix is to replace the gaskets around the valve cover including the ones for the spark plug tubes. Pretty sure your car has 16 of those. Depending on what is in the way of the valve covers it could be a relatively easy job.

5 series and cooling issues. When these cars get old, things like hoses and apparently expansion tanks seem to go out. I would strongly consider spending the big bucks and getting a replacement - even if it means begging at the dealer. The problem with gluing is that you need both a good leak free seal and a strong one that can survive 200+ degree water. If you get the glue wrong, it will come apart again and you will have to clean off the glue to get a proper seal on your next attempt. If it's a non-pressured tank, you can buy some really nice looking aftermarket/racing expansion tanks. If its pressurized.. forget it. Buy a new one.

Most computers are programmed to recognize a certain key. If you had a new key made, it will not work. Cheapest/fastest fix is to have the dealership with the proper computers, reprogram the computer to match your keys. If you have the correct keys, then its possible the module that is supposed to sense the key has stopped working. There might be an emergency work around - ask the dealer. On some cars its some thing like try 3 times, then wait 10 minutes and then it will start. Don't know if or how on a Toyota. Last option, there are tools you can get, usually from the Chinese market places that might allow you to reprogram it yourself For a 1 time job, your probably better off going to the dealer. These tools are typically not in-expensive - and you have to be careful to buy the right one (for the correct market vehicle).

Tough without a code reader. Future reference, most codes go away when the actual problem is fixed. Clearing codes might make you feel better, but the codes typically come back and the cleared codes make it tough for a mechanic (when you finally get it into town). There are some in-expensive code readers that are worth it - if you are handy enough to change a transfer case a code reader should be an easy choice. Since your check engine light hasn't come on again. It might be more of a missfire. Cars made after 1997 are supposed to check for missfire but if you aren't running at high enough loads (full throttle acceleration) it might take a bit to set that light. Make sure all the coils are properly hooked up. You could get an ohm meter and measure out the coils. Chalk it up to bad luck that a coil failed during your other repair. OR If you have most of your troubles at idle - and it runs fine at higher rpm.... vacuum leak There are lots of vacuum lines and I'd visually inspect them all. I would listen for...

I can't say specifically what is wrong - however since you noticed a difference something has changed/broken/worn out. It sounds like your transmission 'thinks' you're accelerating harder than you actually are (even if your not accelerating) and it is commanding the transmission to shift to a lower gear. Modern automatic transmissions (since about 1990) have multiple gears PLUS the torque converter can (should!) lock up when you are cruising. That means at 80kph or so, the tachometer movement should start to match odometer movement.... So if you lightly step on the gas, you see the tachometer move up with the speedometer. Step on the gas hard and the torque converter unlocks and the transmission shifts to a lower gear etc. and you accelerate faster. The torque converter is what allows the car to sit still while the engine is running - call it a fluid clutch. Have the mechanic check all the sensors on the engine. The computer should be able to tell the mechanic what the perceived load on the engine is. A...

The problem with a oil leak is where it is. Often it can require disassembling a large part of the engine to get to it. Open the hood and see all the wires and cables etc. I suspect yours was more of a valve cover leak which is not the worst (Some leaks you have to take the transmission out...... your vehicle is 4WD or AWD and has driveshafts front and rear...) but can still be timely. In the USA, there are standard rate books. You basically look up the job, it tells you how many hours - multiply that by the shop rate and you will know exactly what your bill is. If the mechanic is faster, he makes a bit more money. If he is slower, he looses. Note, if the job requires ... removing spark plugs and the mechanic re-installs new ones. Typically you only pay for parts for incidental work. Often that is like changing the fan belt etc. On some cars, when you change the timing belt, they recommend you go ahead and change the water pump. You pay for the water pump job and add the cost of the timing belt part....

If the exhaust is out (and the torque tube), you can sometimes tilt the engine a bit to get slightly better access.

Fuel sending unit issues are a known problem with early C6s 1) See if the dealer will fix it for you. 2) The factory service manual will tell you to drop the tanks… which means droping the rear suspensionand transmission exhaust etc. You want a lift to do this…. 3) There is a short cut method involves dropping the tank a little and reaching up above and disconnecting the cross-over lines. Then dropping the tank enough to get the sending unit out. Method 3 is documented in a few places including Youtube. Couple of hints a) make sure you get the right sending unit. It has to match the otherone in Ohms (full vs. empty). I would use a scan tool to double check even if the dealer looks it up by your VIN. b) consider doing both sides (sending unit must match what the computer is looking for…) c) If you have clutch or transmission issues, now is the time to tackle that as well. Headers and exhaust can also be addressed. d) Look for a local corvette shop and talk to them about it. They won’t charge you the full...