i dont know any reason you would want anything but the 4:10's. I know towing with em makes it easier than any other truck i've towed with. pick up easy, not much lag on hills as opposed to lower gears will rev the engine up over and over on hills.

 

Mine has 3.73 and pulls just fine plus I would think empty you would get a little better mpg with 3.73. I have heard though 4.10 are much better to tow with a hemi it seems to keep it in the sweet spot better. I for one could not find one vvt 2009 or greater on a lot with 4.10. That might be something you have to order. One thing that might effect there not being many 2012 4.10 is they are now going to have a 6 speed tranny. The top gear and low gear I believe are going to be the same has the 5 speed though.

As far as removing the emissions equipment on a 6.7 and chipping it yes you can do that, but you will lose your warranty. I did exactly this to my 6.7 because the turbo kept plugging up and having issues and was in the shop way to much and my mpg sucked. Once I deleted my truck I had other issues that they would not cover under warranty such as my clutch, transmission, and U-joints. This was only on a 60 hp tune from H&S XRT. The stock DMF is junk in the 6.7 and cannot even hold stock power. Your going to get about the same mpg with a stock DPF based diesel as you will with a 2500 hemi. Unless you delete the DPF and EGR then you are your own repair shop and it is illegal.