I have a 84 nissan 4x4 truck it only thumps in reverse I droped the rear driveline put it in 4wheel drive no thump. is this a rear end problem?
I also lose power going up hill at highway speeds.

check frame mounts.
check l spring bushings and shocks.
check drive shaft monuts and uni joints.
also check tranny mounts..

ok I have checked most of that thanks for the info

you may have to have someone run over you while u are observing..

also check leaf spring bushings and connections..