I'm having a problem with my '90 Cutlass (4-speed auto w/OD).  When it's
cold, it won't shift out of 1st gear, but after driving it a bit (slowly
on side streets), it begins to warm up and eventually starts shifting
normally (actually this doesn't take too long).

I recently changed the fluid/filter and I thought it might be caused by
the cheap (house brand) ATF fluid I used.  So I drained it (I have a
drain plug :-) and filled it back up, drove it a bit and did it again.
I was trying to get as much of the cheap fluid out as possible.  Then I
drained it one last time, dropped the pan and changed the filter.
However, the problem is still there.

Is this a symptom of a dying tranny or is it something that's fixable?

It's a rebuilt tranny w/ 33K and I'm long past the 12mo/12K mile
warranty.  The original tranny lasted 190K miles, I now have 223K miles
on the Cutlass.  If the engine didn't run so well (3.1L) I'd toss it.
But the radiator is leaking now and I don't care for all the lovely body
work my step-daughter has done to it so if the tranny goes then it's
probably time to let it go.  To me, it's kinda like pulling the plug on
a loved one (sniff) because I have run every vehicle I've owned into the
ground.

-PapaRick