Im pretty sure its not normal, atleast on mine. Im woundering if it has to do with the rubber mounts in the A arms. Maybe you load them under hard braking and when you release them they become unsprung causing the clunk. Another thought is like I said before about the transfercase chain having slack. There does seem to be alot of backlash in the drive shaft entering the transfercase. If the rebuild for the transfer case costs 1100 in part, I wounder how much it would cost to put fresh gears, bearings and seals in the front and rear diff, couldnt be that bad. Im trying to keep this truck alive for atleast another 100,000 miles if not more.