It really depends on what kind of off-roading you're going to be doing, but in general, I'd argue that the LSD would be more beneficial on on truck with a factory open diff. Even with a stock ratio, having an improved traction mechanism would help immensely off-road. Regearing while you're doing the differential install wouldn't be a bad idea. Differential installs are fairly complex, and require you to remove the axles, properly shim, and adjust backlash on your gears to ensure no issues.