Just had the tranny overhauled in my 69 340 Dart.Car is all stock.Had them go ahead and throw a Transgo shift kit in it.Told them nothing to radical as its bone stock.Some thing along a RV shift kit Get the car back and after a few days I stomp on it from a 15 mph roll.It drops to first and the rpms climb well past 6k and I have to get completely out of the gas for it to upshift.Thinking that was weird a few days later I manually shifted it at 5500 and the rpms once again kept climbing well past there.Thoughts? They do have a warranty for a year or 12k miles.

PM John Kunkel if he doesn't see this thread.

Is your kick down linkage adjusted properly. Sounds like too much line pressure. Try shortening your linkage a couple of turns and see if it helps.

Adjustment, let them do it that way they are responsible, if you go monkeying with it they refuse warranty. Linkage out far enough can burn up a unit, your's is probably fine at this point but they need to make it right, you paid them and trusted them to build it, trust them to fix it right.