Auto transmission won't shift

[Dudd]

Alright, I'm pretty much resigned to the fact that the tranny is going bad, but figured I'd post anyways. I've got a 98 Old Silhouette, and the transmission has stopped shifting regularly. It'll just rev up to 4500 RPM, and then it will finally shift. Anything that will be causing this to happen that doesn't require a new transmission? For the record, I barely drive this more than 2-3 times a week and never more than 5-10 miles each trip, usually less.