1500 Runs Rough in Overdrive

I have a 1991 Chevy 350 Automatic. I have noticed over the past several months that,when shifted into overdrive, engine begins running rough. However, if I shift back to drive, engine will run smooth again. Sometimes I can drive in overdrive with no problems, but otherwise it gets pretty jumpy until I shift down. Any ideas on what could be causing this problem?!!

could it be the torque converter trying to lock up but repeatedly not being able to?

Sounds to me like your converter may have packed it in.

nope not the converter... check the plugs and wires ... sounds like a miss to me in fact i would almost gaurentee a miss.. that when you can feel a miss the most is under a pull like in overdrive.... torque converter is fine.

This is a stretch but it's easy to check. I had this problem on my '95 Z71 where under light load in OD (slight grade hill) the truck would downshift into 3rd then shift back into OD very rapidly. Eventually I found the coil wire (center post on the distributor) had corroded and I was getting inconsistent/weak spark. It may not be your problem but it sounds similar.

had the very same problem with an 85 chey. ran smooth until it shifted into overdrive, then the while truck would shutter. check the torque converter to flex plate bolts. 2 of them where loose on mine, tightened them up and the problem was gone.