If your serious about non-street driving off-road deep mud fun I second the agricultural tire option. Ag tires come in virtually any diameter, width that you would want but you may need some adaptors to adapt ag bolt-pattern wheels to your truck lug pattern if you cant find truck wheels with the right diameter for the diameter/width tire your looking for
Otherwise if price is your main criteria, if you can fit 37's, military humvee wheels/tires can be an extremely cheap option that has the same 8-lug pattern as our trucks. Otherwise lug adaptors are easier to find going from GM 6-lug to GM-8-lug rather than trying to find or custom make ones for ag wheels. And the military tires are DOT legal for street driving
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