stumpled

just bought me 89 4.0 auto xj last tuesday. been driving it runs fine. drove it to go 4 wheelin and ran fine. while wheeling going up a trail on mountain at a slight incline the jeep started running like total crap would barely even move. so put it in nuetral reved it up ran fine. put it in drive goes about 10 feet fine starts running like crap again. put it in 4 hi runs fine the rest of the way up the mountain. get to top put back in 2 wheel. runs fine drive about 15- 20 minutes come to another slight long grade same thing put in 4 low runs fine. on way home on highway come to slight grade and at the top starts running like crap a little gets to top runs fine rest of the way home . wwhat gives

Where's the fuel pickup? Could be you're pulling some water off and on while on an incline...