After having the cooler line changed I noticed slippage on the 3-4 shift, checked the fluid and found it low (I only drove it maybe 50 miles).
Went back to the dealer and they put 3 qts in it to fill it. Hmmm still slipped or very slow shift. They had thier tranny guy take it out with a tester plugged in and he said there was no problem showing on 2 test runs.
The dealer has been pretty good with me so I dont disbelieve what they said, and I'v never limped it or had any codes show.
They told me to keep an eye on it and maybe the trans was in a relearn mode (I had towed my 5th wheel for 7-8,000 miles with no problems) and as a last resort would reflash to start over from square one, but it isn't a good idea, so they say.
I have 32,000 miles on the truck with the 5yr 100,000k GM extended power train warranty (I'm Canadian)
It only seems to do this when cold and not when tow/haul is engaged.
Any suggestions?
Thanks for any input.

Peter

I ahve had some crazy things go with my ally, sometimes it would downshift hard and sometimes it would take for ever to shift, it wouldn't repeat this everytime and the dealer told me that when i load the trailer on it, it goes thru the learning process, and when it is unload it relearns again. I have almost 200k miles without any problems and am running amsoil tranny fluid. The shift from 3-4 makes me alittle concern but if you use the tow/haul and it does it I would be concerned if it repeats it everytime.

There is another post about this here. Pretty common on the 06 it seems

http://www.dieselplace.com/forum/showthread.php?t=155635

Thanks guys, I feel a little better now