my tires are titan R4 10-16.5 front and 17.5L-24 rear. The pressure recommended in tha manual for the front is 20 psi: I keep mine at 30 psi: could this be the cause of the bouncing?
I would suggest not ever running it in 4 wheel drive on dry pavement. You will end up repairing something in the drive train. When it bucks like that, its trying to tell you that you are about to break something.