Dead Truck???

I have a 75 K20 with a new 350 motor in it. When ever you put the truck in any gear except neutral or park the rpm drops and the truck dies 5 seconds later. The truck has a perfect idle when in park or neutral. I would guess that the rpm drops to about 500. Any suggestions???

Check your timing, a out of time engine can idle fine in a no-load situation. also check for vacuum leaks.

Might have a fuel problem too, the rpms are supposed to drop a few hundred rpms when u put it into gear, but something is causing it to stall because it cant run with the engine turning that slowly.

put a vacuum guage on it, it should run between 18 and 21 inches of vacuum at idle.