Overdrive problem

Car shifts fine first to second, second to third always. When shifting from third to overdrive it often slips, the tachometer shows the rpm indicator is waving around. If I punch the gas peddle it sometimes makes it shift. Going uphill it downshifts okay, but then wont return into overdrive till about 5000 rpm's. I recently had the transmission fluid and filter changed as the fluid was clear, now it is pink again and transmission behaves slightly better. They found almost no metal filings in the pan. Also tried some GM transmission additive little improvement. Is this indicating the over drive shaft splines are worn or is it worth trying to change out the pressure and shift solenoids?