Truck won't start after driving but will if you let it sit and cool do

I replaced starter battery alternator starter syliod on the fender but it will start but after you drive it and shut it off it won't start back up it don't have the voltage to turn the engine but if you let it sit for hour or so give or take it will start up again slowly then kick back into it and when it is running the if you run the heat or ac it will drop the voltage gage and oil pressure gage will go high what could cause this issue been trying to figure it out for while now