There is no easy way to identify the problem. The only sure way is to put it up on jack stands and pull everything off. Then start by measuring the spring mounts to the outside edge of the body and both to the front and rear of some random point not affected by the accident. You need to make sure they are still square with the body. Then you need to look for a twist at the ends of the springs and measure the length and look for any twisting. A bent spring can also throw it out. Or just replace them. Then you need to check the axil thoroughly. look for stress cracks, look for any possible bend or twist or just replace it too.
It will not be the shock. It will not be a bolt on part like a sway bar. It could be the drag link if you have one after the lift. The lift would have thrown that off center so they had to take the original off or replace it with one from the kit. A cheap kit may not have had one.
Also consider you are now adding another angle to the already poorly aligned drive shaft because of the lift. u-joints are to account for minor alignment issues from a suspension. They are designed from the factory to be in a straight line from the tail of the transmission to the rear end. Now it drops to the rear end because of the lift and is off center because of the accident. Expect driveshaft, u-joint, transmission or pinion gear problems if you do not fix it. I have seen the entire tail of transmissions being destroyed because of a bad u-joint on a lifted truck.
My rule of thumb is to sell any vehicle i own after anything more than a light fender bender. You could have easily bent the frame. It would not take much. And then mounts start to fail along with mysterious creaks and groans in the plastic parts along with cracks where screws go, transmission problems, etc etc etc. If you jar a car hard, you will do all kinds of minor damage that will turn into big problems later on.
If you love THAT truck, spend the time and money to fix it. if you love a truck LIKE that one, sell it. This is just the potential tip of the iceberg of a ling list of potential problems.