2001 Astro problem...

When acclerating from 0-40 mph at regular intervals I can feel something "catching and then releasing" in my van. I can really feel it when acclerating hard, like merging onto the highway. The faster I go the faster the "catching and then releasing". After 40 it seems to stop or at least I don't feel it because of the speed. It seems to be coming form underneath between the driver's and passenger's seats. Transmission fluid level is overfilled (idiots at Wal-Mart lube and tire). This problems just started and the van only has 60,000 miles on it.

My guess is that it either isn't shifting right or the torque convertor is locking and unlocking because the tranny is over-full.

I have a AWD 2001 Astro that was doing the same. I changed all (rearend, frontend, and tranfer case fluids to syn. 75/90 and that did it.

I know this may be a stupid question, but is your air conditioning compressor kicking in? On AWD vehicles, this can cause major changes in engine torque which can cause the transfer case to change from engage to slip to engage. Just wondering, sometimes we miss the obvious! Turn all of the air controls to warm, run the blower fan, and TURN OFF THE DEFOG/DEFROST. Did it stop?

seabuzz,
Did you put 75/90 in your transfer case? I thought you need the special blue GM fluid.