88 Grand Caravan Shifting Problem

I have an intermittent shifting problem. Sometimes it shifts up/down, just fine. Other times, it stays in 2nd gear, no matter what the speed. It will stay stuck, even when stopped. I don't do much freeway driving, just daily city driving. I've heard of a "learning" feature, in the computer, that governs shifting, based on driving habits. I'm wondering if this might be part of the problem.

Details: 88 Grand Caravan, V6, auto trans.

Thanks...