Modulator?

Any major electrical "issues" can cause this...Coil pack battery ground. When you are having problems it is always safer to get a mechanic you trust to go over it so you have a second opinion to your own or other people who may have given you advise. If you cant spend the money for a diagnostic, then do one yourself. I mean go over the car checking every part that may be causing the problem. It is truly the only way to go. After checking every part and you are still not sure where the problem is weigh the cost of replacing parts until you fix the problem against a good diagnostic. Mine was the negative battery terminal on my "new" battery. This also caused a drain on my alternator and killed a few of them. Actually I could get a nice lumpy cam sound out of the car when the juice was low. lol No performance though. Best of luck. Remember to check all the inexpensive areas first.

Another thing, I have the torque converter lock up in both OD and D, and both exhibit the same symptoms of not wanting to unlock.

My car has 140k on it, and I talked to my dad (he had the car before I did), he said it's been doing it for at least since 60k miles or so.

My '92 SE does that as well. The 4T60E (found in both our cars) likes to lock up the torque converter and not release it under light load. I'm told it's a design flaw with the transmission.