If I upgraded to a 37 12.50 would the tires still rub? I trimmed the front bumper on the bottom so that it would eliminate any rubbing on the bumpe
It's tough to say. Even though your width would remain the same as what you currently have, you'd be increasing the diameter by 2 more inches, which could have interesting effects when you've got the wheel turned all the way in one direction, when your shocks are compressed, and most probably when both occur at the same time.
You should probably take some measurements with your truck in each of those conditions and see if you have 2 more inches of clearance. It won't be a perfect answer but it'll give you a pretty good idea of whether or not you've got more trimming to do if you upsize by another 2 inches in diameter.
With tires the size you are looking into it isn't the back I would be the most concerned with. It's the front! The front IFS suspension is at the upper range of being capable with 35's. 37's to me is asking for trouble. Why? The added weight of the tire which adds additional stress to what concider a "weak" suspension. If you plan to wheel this at all you will be replacing parts real quick.