This was my grandfathers truck that he purchased new and drove until he passed away 10+ years ago. Its a 1984 GMC w/ 305 automatic. My grandmother still has it, and still uses it occasionally. Its only got 47,000 miles on it, and my grandfather kept up the maint as it should have been (which wasnt much with so few miles).

anyway, Sunday I did the normal plugs/cap/wires/rotor/air filter maintenance on it because it was just time. It was beginning to show signs of needing it, in addition to a hesitation problem, so it was done.

afterwards it runs GREAT, but still has the hesitation problem. Seems worse when its cold, but it still does it after driving for 50 miles.

Basically its either a hesitation issue, or a shifting issue. Only seems to happen in the 1 -> 2 shift. Floor it, truck goes fine until it gets to the point where it should shift, then the engine just seems to fall on its face, and stay there. It will chug as long as its floored, and wont stop/shift until you lift off the pedal. Then its fine. Floor it while cruising (ie in 3rd gear), it down shifts and goes, and shifts with no problems.

Any ideas on what the problem could be? truck is completely and totally bone stock. I went through most of the vacuum lines and replaced what bad ones I found but that was no help. Trans fluid is nice bright red, and full.

thanks,
clay