I'd second Frontier Gander's solution. Others that will do the same thing is a no-slip or lock-rite locker. The other thing that you need to look at is tires. Having the right tires will make a huge difference. You didn't say what truck or tires you have, or how often you're in mud, but my recommendation would be for Goodyear MTR's or BFG MT's if you're in mud a lot. When driving in mud, you don't need to barrel through it real fast and spin your tires either. Your best bet is to just keep the truck rolling and let the tires do their job.