Q: 4wd engages but vehicle bucks like 4wd is slipping.

There is likely an internal issue going on within your transfer case. The most common cause of transfer case slippage is low fluid. I suggest that the transfer case fluid condition and level is checked. If the two wheel drive mode works just fine then it is more than likely there is a fault in the transfer case not the transmission itself. I also suggest that a technician check the shift linkage from the 4 wheel drive shifter to the transfer case. Make sure it is still in proper adjustment. Another way you could test the transfer case is by removing the shift linkage and moving the transfer case through the four-wheel-drive functions by hand. If they feel any trouble with it going into the separate gears then that helps further indicate that it is a transfer case issue. Usually a four-wheel drive fault will come with some type of indicator other dashboard and or a code stored live in the vehicle computer. A technician such as those we provide here can run a scan diagnosis on the transmission module of your vehicle to get some clues as to what the problem could be. I will ask customer service to send you an estimate for a four-wheel drive malfunction diagnosis.