popping in rear end

i just got my 88 cherokee back from the shop.had 4:56 gears installed,detroit ez lockers front and rear.after driving it for a week,all of a sudden my back end pops and jerks a bit to the right,then it will pop again and jerk a bit to the left.sometimes it just clunks hard all together.this is under normal freeway driving,smooth roads.it's completly random but does it a lot.i've had lockers before and this doesnt feel right.dana 44 rear axle by the way.the first week i had it back it was smooth as can be.i broke in the gears the way they said and did no off roading.the shop will warranty it but just wanted to see if this ever happened to anyonee else before.thanx