Take a look at the u bolts. Inspect them and make sure there is cracking, deep pitting, or major rust (other then mild surface rust), replace them. If the bolts are in good shape reusing them shouldn't be a problem, but look at and inspect the threads, If the threads are stretched or damaged, replace. If you do reuse them, make sure you use new lock nuts. If you are unsure on checking anything, then don't risk it, replace them. Also, if you are using your truck for off road, or hard work, replace them. If you are using the truck for the occasional small load or just a DD, then reusing them should be fine if they check out ok.