GM or Ram? Help with my decision

Hey all, I'm going to be buying a new truck in the spring and while I've currently got an 04 Ram 3500 CC with Cummins diesel which was my first Mopar vehicle and one that has been an amazing truck, in my youth I was strictly a "Chevy man". My new truck will be a diesel 1-ton 4WD crew cab long bed, single rear wheels, top trim level. Since then I've owned all 3 American truck brands and I feel they are all so close and good trucks that it's making my decision sorta difficult. The Ford styling I do not like so it's out and the new Ram's interior is second to none as is in my opinion the Cummins engine, BUT GM stepped up in 2015 with their interior which I think has closed the gap big time between it and the Ram. The other thing that is pulling me towards the GM is the Allison transmission as I pull a 15K fifth wheel and transmission issues have been a concern for my Ram and the Ford I had prior to the Ram. So I'm on the fence now between the Chevy and Ram and was hoping to get some input that will help me make my decision (no Ram bashing please, really all 3 brands are good trucks with their own issues as is natural).

So I have a few concerns about both the Ram which I'm addressing is a Ram forum and the Chevy which is why I'm here. So here are a few of them and hopefully you all will be kind enough to comment on them.

The Chevy has the squared off fender openings and I would want to install 35" tires without a lift kit although a leveling kit to bring the front height up to match the rear would be an option. Will the Chevy accommodate a 35" tire stock?

I've had several Chevy owners tell me their trucks had squeaks and rattles in the cab that they couldn't resolve, granted these were not the new interior so are those no longer an issue with the 2015 new "soft" interior?

Has anyone heard whether GM has any plans to eliminate the DEF system? There's a rumor to this effect going around. I really dislike the appearance of the tank under the passenger door.

Those are my two biggest concerns but I'd love to hear from anyone about what they like or dislike about their Chevy/GMC Duramax heavy duty trucks so I can get a feel of what the new GM trucks are about. Thanks