I have a 2004 Buick Rendezvous with 214,000 miles. It has been a great vehicle and I really have not done anything to it except the ususal scheduled mainenance.
I changed the transmission fluid every 30,000 miles with no problems until the 150,000 change. As you have probably guessed by now, when I changed the trans fluid this time it started shifting rather roughly at times.
I spoke to a mechanic who explained that that essentially, the gunk in the trans fluid was actually helping the shifting (clutch) and when I changed the fluid I lost this extra grit and thus it started shifting roughly. He put in a transmission fluid additive and that did the trick.
My problem now is that I have not changed the fliud now since the 150,000 and I have 214,000 miles on the vehicle. As you can immagine the fluid is getting a little dark and I don't know what I should do.
Do I change it again and add the aditive again? Is there any way to change the fluid and save the Gunk? Am I at eh end of the line and looking at a new tansmission. It really runs fine right now with gunk and dark fluid.