I have searched already and could not find any answers to this. I see that it's quite popular to level the front of the trucks with the rear height. My question is if this is done have you up set something? As far as I have seen every truck from every manufactorer comes with the front end lower that the rear. I'm no engineer, but I think that this is done so that when the rear of the truck is loaded that the rear and the front are at or near the the same ride height. So that handling is still good. If you level the front or your truck with the rear when it is empty and then load it won't you have a situation with a front end that has to little weight on it? And then it won't handle right.
And wouldn't this condition be even worse at highway speeds.

 

It's done intentionally by Toyota, but I haven't heard of adverse effects from leveling it out. There are two ways to level - the first involves shackles in the rear to lower it. The other (which I am doing when the parts arrive) uses coils from Wheeler to raise the front end up, which also stiffens it somewhat. The coils are $200, unsure what the lowering kits cost.