Still another tranny problem/question

[mile-hi-bri]

'92 w/about 75,000 miles on current tranny.
Good shifts in ALL gears, but slips ONLY in 4th gear and ONLY under moderate to strong acceleration.
Doesn't matter whether t/c is locked or not.

Adjusted trans band,(twice in life of trans so far), clean/fresh fluid and filters(aftermarket filter too).
Has Small Car shift kit too.

Does this sound like bad band or perhaps a solenoid, or, etc.
I thought 3/4 used same band/drum, so shouldn't it slip in BOTH 3 & 4?
Confused and frustrated and...?

Any ideas?

Happy Holidays to one and all!!!