unless you were abusing it badly by redlining or not shifting well or i suppose maybe burying it in mud deep enough to cover the tranny you sreally shouldnt have damaged the tranny. it is possible if you bottomed out on something right on the tranny you could have fucked it. Is this s new truck? how many miles on it? manual or automatic? does it drive differently now, or does it shift really hard? take it and get the transmission fluid flushed and replaced. and learn a lesson taking a truck down a 4 wheeler trail is not a bright idea for a couple reasons, a 4 wheeler trail is usually a lot narrower, unless yo uknow how to trail ride it is never a good idea.