A truck LS has a tick, a misfire, and the rocker arm on that cylinder is loose. Is it a collapsed lifter, and what does the repair involve?

That combination (tick, misfire on one cylinder, loose rocker on that cylinder) is the classic sign of a collapsed lifter, most often an AFM lifter on Gen IV trucks. The repair: the heads have to come off to reach the lifters. Replace all 16 lifters and the lifter trays; inspect the cam lobe (a failed lifter can grind it down); check pushrods for bending; and if it's an AFM engine, consider a full AFM delete (non-AFM cam, conventional lifters, blocking the oil circuit, a tune). You'll also need head gaskets and head bolts.