a/t don,t upshift easily.

base prizm a/t don,t want to upshift from 1st to 2nd and from 2nd to 3rd easily. if i let up off the gas at 20 mph for a moment it will quickly upshift to 2nd.then at 35 mph let up to shift into 3rd. otherwise it just revs up alot untill finally it upshifts.car has 165,000 miles on it.original owner serviced a/t twice. anyone having this problem?