Delta 88 rough idle +

This has been very interesting so far. I have reviewed many of the posts and they have helped improve the car, but still having some troubles. Thought I would post my symptoms and see what insight others have.

Things I've tried: Plugs, wires, MAF (was getting code 34, thats gone now). Currently no error codes for 2 days, but problems below persist.

Car runs great until warmed up (about 10 -15 minutes) then:
1. Rough idle and rough accelleration - feels like a cylinder isn't firing. I've replace plugs & wires
2. Again, after its warmed up, I also begin to feel a deep vibration (maybe once every 5 minutes) when under power anywhere between 30 & 55 MPH (if I let up on the gas it goes away for a while). It feels something like a driveshaft problem I had on another car, but its not pulling to the side. I'm afraid its the tranny. Also, this goes away if I shift down from "D" to "2"

Any thoughts are appreciated. Especially, is it possible for these two problems to be related?

Thanks . . . these forums are really great!