your stock tires are 34.1", you will be able to go with a 35 without problems and 37 with a leveling kit, the toyo open country m/t in a 35x12.50x20 has an actual diameter of 35"
a few other options:
the cooper stt comes in a 35x12.50x20 with an actual diameter of 34.7" and is a very similar tire to the toyo open country m/t
the pro comp xtreme m/t, this tire comes in a 35x12.50x20 and is an actual diameter of 34.6", I am currently running this tire on my truck in a 37 and have been impressed so far but I do not have many miles on them
hope this helps