If you have P/U bushings in the back, remove wheel, loosen the non-camber controlling bolts, jack up the control arms by the knuckle to where the car is about to lift off the jackstand, then retorque the bolts. Release the jack, reinstall the wheel, do the other side. You want to torque the suspension hardware while its loaded, not at droop.
The jerking could be lugging the engine because of the flywheel. Digging out of a turn could do that. If it starts going down on power,it may be something else.
That shifting issue *sounds* like hydraulics. Could be s pedal adjustment issue (unlikely).