Won't shift past second gear, only shifts from 1st to 2nd.

What is your question?

Sometimes it doesn't shift at all, and it doesn't ever shift past second.. Can't go over 40mph, and that's with it revved to the max.. Thinking it might be shift synchronizers, Not sure...

What makes this problem better or worse?

Doesn't seem to make any difference, hot or cold

How long has your 2001 Isuzu Rodeo had this problem?

Few weeks