Tranmission problem

I have a 2002 Astro LT with 26,000 miles on it but the transmission shifts hard and klunks when going into overdrive. This only happens in very cold wheather -10 degrees to aprox 20 degrees above. Anybody have any ideas? I have had it into the dealer with no fault codes in the computer and it did not act up when it was there. It seems that after it warms up its fine but really shifts hard ito over :) drive when cold.
Jim E

I have a 2002 Astro LT with 26,000 miles on it but the transmission shifts hard and klunks when going into overdrive. This only happens in very cold wheather -10 degrees to aprox 20 degrees above. Anybody have any ideas? I have had it into the dealer with no fault codes in the computer and it did not act up when it was there. It seems that after it warms up its fine but really shifts hard ito over :) drive when cold.
Jim E
I don't know if this will be of any help but I have a 1994 Astro which I have synthetic oil in both the engine and transmission. The viscosity is not affected by a tempertature change as much as regular oil. My van turns over below zero just as fast as it does at 50 degrees. Maybe your transmission fluid viscosity is to high at the lower temp. I know it shouldn't be enough to make a difference but low cost fix if it will.

Does your van have the "Haul/Tow" option? Mine does, and when I use it, the shift points change and the engine / transmission shift much more agressevly. MAYBE the system switches to the Haul/Tow mode when cold for some reason, even though you haven't selected it. You could test by switching to this mode yourself and see if the van acts the same way you describe.