So lately, right after starting the truck, if I decide to go drive before it's fully reached temp and gotten to at least 130 on the vague, it acts like it wants to die anytime I let off the gas, immediately it will go to about 400rpm and barely stay alive. Any ideas on what could cause this?

 

Could be many reasons. These are in no particular order.

Old worn spark plugs
Failing IAC valve
Failing TPS
Dirty or failing injectors
Failing fuel pump

 

What year? What engine? Please add this info to your signature so we don't have to guess.

 

2001 Truck, Engine is a 5.9 V8 from a 98 Dakota, was fully cleaned and tuned up and put in my truck about a 18 months ago, have done regular maintenance on it since and its been running fine until just recently. I would've added it if I thought those specifics would be relevant since im asking more general, I'm sorry