truck dies when put in gear

I just got through taken out ac/heater and when I try to warm the engine up to temp to flush radiator, I put it in gear and it dies. As long as I have foot on accelerator it will stay started but when I'm driving and I let off accelerator it will die

hey man u might try gettin your alternator checked. my tahoe did the same thing when my alternator went out. so my first guess is thats goin out. Peace out.

nevermind, Not sure what it was but i had also clean my K&N and had sprayed the oil on it. Maybe the oil was clogging the air flow. Don't know but it seems to work like it did now. but now i have no taillights and no brake lights so someone is trying to tell me not to take the truck this weekend

This is whats happenin to my 93 Jimmy I just bought, it of course ran fine for 200 miles on the way home and now i have to keep the foot on the gas to keep it running. Guess i might try a alternator like the guy mentioned above. Any other ideas??????

if you ever messed with the spot your ecu comuter is located you may need to adjust the idle on the computer theres normally an adjustment on the side of the unit to add or take away fuel

Well for some reason I'm having the same issue even after replacing the temperature sensor. Does anyone else have any ideas besides adjusting the idle? I'd greatly appreciate them cuz I just got my new tires mounted and I'm ready to actually drive it!!!!!!!!1

if your truck has no brake lights and taillights its your multifunction switch or stop light switch which ever you wanna call it what year truck is it?? and also for the other guy check your throttle position sensor