One problem related to power train has been reported for the 1998 Nissan Frontier. The most recently reported issues are listed below.
I have a 98 Frontier which has twice in the last six months inexplicably reved the engine, on it's own, to almost 6000 rpms in conjunction with this is an increase in speed. The first time it happened I had just left a garage from having a tune-up & oil change. The next was on a very narrow country road. It didn't matter what gear it was in , I have a 5 speed, or reverse. It is very frightening when this happens & the mechanic can find no reason for it. I worry about it happening in the winter on icy roads. This is an accident waiting to happen.