I might have a few things for ya on that if i can get this wriiten again before i get bumped off ok , when the wheel jerks or surges especialy when parking the following should be looked into low oil duh , loose pump belt, insufficiant pump press.,to check pump press. install gauge inbetween pump and high press. side of hose at operating temp bleed system by turning wheels against their stops for a min and then turning the other way, repeat a few times bringing fluid up to temp 150 to 170 degrees, refill res. if needed and start engine pump press should read between 80 to 125 lbs. if higher up around or abouve 200 lbs. check the hoses for restriction or popett valve , it could also be a faultygear relief valve, check the flow control valve for sticking ,also bring pump to oper. temp again then check your fluid, if its milky or foaming then you have air in the fluid probably internal pump leakage or a hose or air leakage in the reservoir line.
If your symtoms are more like kickback or loose steering which it sounds a little more like then again look for air in the system, steering gear loose on frame , out of adjustment or worn, steering stablizer loose or worn, linkage loose or worn, check the idler arm especiuly, that is my guess, check all fasteners especuily if you have a lift, mine seem to work themselves loose ,even with lock tight i double nutted a couple on high stress points and peened the inside edge just for g.p. if all that is good then check your wheel bearings for adjustment and wear. alot here but i figured i would give you it all and you can apply it as your symtoms describe best good luck HAMMER