Something you may want to try and it's a whole lot cheaper than anything else is to simply change your diff fluid. Use one specifically for the LSD. You may be surprised that after you change the fluid your LSD starts working quite well. I've seen many LSD's that had the wrong fluid in them.
'94 F150 XLT, SC, LB, 4X4, 5.8, E4OD, 3.55 LS, 16" Tires