Transmission problems at low speed

I have a 1998 Chevy Prizm with 144,000 miles that I just bought used. Yesterday I noticed that when I accelerate up to about 25-30 mph, the (automatic) transmission revs really high before finally shifting. It does not seem to have any problems once I get going faster. The check engine light is on, but the fluid level looks okay and there are no leaks that I can see. Does this sound like something that will be a relatively easy fix, or should I brace myself for something big and expensive?

First things first. Go get the codes read. The problem with your transmission shifting could be transmission related or could be engine related, like a TPS for example. We could guess all day long but our answer just might be there with the check engine light.

transman