Trans shifting weird

[mike_dmt]

So I've been lurking around to see if anyone else has this problem: it's an '01 4.4..

A while back, I had been experiencing some RPM fluctuation at in-town cruising speeds of 35-40mph. It was relatively minor, maybe +-50 RPM. It was hardly noticeable on the tach, but I could hear it.

So, I had the trans filter and most (haven't drained and refilled again yet) of the fluid changed about 5k ago. Also had the dealer do a software update.

Now after driving it until it's warmed up, it will downshift on its own from 4th to 2nd, even if I put it in manual and try to upshift, it will stay in 2nd. It doesn't do it until it's good and warm. Maybe 30 minutes to an hour.

Unfortunately it's somewhat intermittent. Some days it's perfect, some days it's a PITA.



Any ideas?