37s rubbing on the inner fender liner is really dependent on two things, tire size/lug design, and wheel offset. Generally speaking, you can install 37s with the correct offset wheel and only have to do very minor fender liner trimming, if any.
As far as power loss with 37s. Anyone who tells you "I don't notice any difference" is either lying or hasn't paid attention at all. The OEM power wagon wheel is just under a 33" tire, so a 37" tire is 4" taller, or over a 10% difference between sizes. That isn't to mention the weight difference.
Now, that's not to say that it's untenable, a lot of folks run 37s without regearing, especially with the new 8 speed, but it will be noticeable.
I don't have the hemi in my truck, but I did notice a difference in acceleration. I would still do it again, but it was clearly a loss in acceleration.