I'll second Dave - he seems to have the right plan.
I run the Toyo Open Country A/T on my '92, which sees mostly on-road (mix of local and highway use), and some light off-road activity. I haven't tried much mud yet either (lot of trouble to get off, I've heard), but other than that, they seem to handle fine on the trail. They've got about 30,000 on them, and from the looks of them they've got about that much tread still left. I'm pleased with them, and would seriously consider getting them again.
HTH,
Rob