Transmission Shift Between 3 and OD
My vehicle is shifting between 3 and 4 like it can't decide which gear it should be in. This occurs with slight acceleration while climbing to a good steady speed. Appears to be more prevalent in the first 15 minutes driving. If I manually shift to 3rd to keep it out of OD it seems to drive normally and not jump around. I don't recall the RPMs jumping wildly either. I had the surge transmission problem (bore and piston leak?) fixed under warranty, but that was about 100,000 miles ago. This feels different, and it is occuring when cold, not just hot running conditions.
Lets just assume that my fluid and filter are filthy dirty since they haven't been replaced in the last 100,000 miles. So I'm all for changing my trans fluid and filter, but is there something else I should be looking at first? Just don't want to spend a hundred dollars on fluid flush to find out I have another problem in there to fix.
97 Bonneville SE, 125,000 Miles. Not supercharged.