It's been happening for a few days now on my '98 Ex Auto sedan (LX: American).. but only from time to time..

I rev up to about 3k rpm whenever I drive so no hardcore redlining, when I accelerate, the car sometimes doesn't upshift and keeps reving up to about 5k, then shifts.. seems as if there's a lag between the shifts.

Can anyone help me out? I recently did a major tune-up, tranny fluid changed..