Starts Fine and Stalls

[USArmyCombatMedic]

Hi all, I am new to this forum so please bear with me. I have an 87 Chevy R10 with a 350 and 700R4; 80,000 miles.

I have no idea what the problem could be hoping you guys can help. I bought this truck about a year ago. At that time it ran great but it would die at idle if it sat there for a while such as at a stop light. The truck would also shift hard into first and reverse, sometimes causing it to stall itself. That's when I gave up and left for a years worth of training for the Army. Now Im back and trying to attack this at a different angle.

I tore the truck apart and have rebuilt it from the ground up, completely new suspension (8 inch lift) system, brake system, steering system, frame is all painted, rebuilt transmission, rebuilt torque converter. I tore the truck apart figuring the stalling was caused by a faulty converter, lo and behold I put it all back together and same problem. Shifting is great in everything but P to D and P to R. Truck still stalls if I do not give it gas such as a stoplight.

What problems could this leave? Fuel, Air, and Spark correct? Took it in for a tune up, new plugs, wires, distributor cap, rotor, timing was redone. The problem persisted, mechanic said get a new distributor assembly. Have not got it yet since they are a bit spendy. New starter.

The air category is a bit mysterious. I went through and researched this. It all seems to be correct, no vacuum leaks that I have found. If I disconnect the intake manifold vacuum line from the cruise control vacuum line it produces good vacuum and will run for a minute or so (really low idle) and die. If I hook the two vacuum lines up it will start and die within a few seconds. What is up with this?

Then there is the fuel category. New tank, new lines, new filter, rebuilt TBI, the only thing this could possibly be is fuel pump correct? Since the injectors work great and spray a cone pattern like they are suppose to.

Like I said I have researched this a lot. People say disconnect the torque converter switch to make sure you did not screw up installation- no difference. Check EGR valve- stalls when compressed. Check coolant temp sens.- removed no difference. New IAC- no difference. New TPS- No difference. It will not throw me any codes other than the 12 I am suppose to have.

I am really stuck here, I have a lot of time and money into this and don't want to continue if it will be a problem truck the rest of its life. Any help will be greatly appreciated, I am only 20 so bear with me on vehicle knowledge please. The only potential fixes I can see here is new fuel pump? new distributor? recheck vacuum lines? None of these seem to make good sense to replace though. Thanks in advance.