Speaking of cables and adjustments... I thikn we had this same kind of issue when we purchased a tranny for my Uncle's '96 GT - but we think we've got it fingered out now. Just gotta get the time to make the adjustment.

We had to replace the linkage on the tranny when we installed it, and put the one from the car onto it, b/c the tranny was from a newer GT, so one was round the other was square. Once we got it in, we had to change a few sensors, and the speedo gear. Got it all buttoned up and then the tranny would shift AWESOME under full-throttle and manually shifting, but then with it just in "D" it would over-rev going into OD. Talked to the guy from PA down at NMRA, and he told us to adjust the line pressure at the linkage. He thought we should've known about that, lol... Damn rookies