Prfoblems in AWD

I only use the awd when the roads are wet. Last week we had a lot of rain so I turned it on. Everything was fine until the trans hit second gear and then the truck started to buck slightly while accelerating. It will not do it in first, third or od. 2wd is all ok. Almost feels like the engine is missing. Anyone seen this before?
03 ltz
Thanks for any helpful replies.