the stock gears should be 4.10. I have 33s with my stock gears and do just fine. I drive on the freeway everyday and do better than I did with 31s because the bigger tire brings 3rd gear into range alot more. I noticed the power loss when I got the 33s but after a quick tune up all power was regained.
oh and it has plenty of power to go through the mud high or low range

erick

85 Pickup
33s, lift, EB cam, header, exhaust...