Hi everyone-
I have a 93 Impreza wagon, 1.8L 2WD automatic with about 150K on it.
For the past few months I've been having a problem where it takes close
to 10-20 minutes at highway speed (55-60) before it shifts into
overdrive.

I've noticed the car has some sort of mechanism that keeps it in 3rd
for a bit before shifting into 4th if it's particularly cold and the
engine hasn't warmed up yet, so I usually take the long way to the
interstate to let it warm up a bit. However, the car doesn't still
doesn't want to shift into OD once I've gotten on the highway with the
engine fully warmed up. I've noticed this problem occurring even when
the weather hasn't dropped below freezing, but it seems now that the
temperature is lower it takes even longer to make the shift to OD.

It's driving me nuts, because the car stays at 3000 rpm in 4th and
absolutely refuses to go into OD even if I speed up slowly to try to
get it to shift... or slow down/speed up, rev the engine, etc... so
basically I spent my entire commute in 4th and then 1 minute in OD
right before my exit. Maybe I'm being paranoid, but I feel like it's
also killing my gas mileage.

Any idea what could be causing this? I had my transmission fluid
changed last month, and I'm up to date on my oil changes/etc. The only
recurring problem with the car is a slow leak with the power steering
pump, but I doubt that has anything to do with the delayed shifting.

Thanks!

-Kendall