It's not un common for trucks today, under light load to use the rear brakes more then the front, this is to off set wear under heavy loads. GM SUVs and trucks have this wear pattern quite often. Our f-550s in our fleet trucks see higher rear wear then front wear. I think 35K seems a little quick but I don't know what you are hauling/towing or your driving style. I'd say you can expect to see between 40 and 80 out of 1/2 brakes and 80 to 100K on 3/4 ton brakes (majority non loaded miles). Our 20K mile expedition has about 80% brake life on it but it's all highway miles too, I mean drive 150 miles use the brakes twice and then drive another 150 and use the brakes twice kind of driving.
I'm mostly in the F-150 section, but I replaced my rear brakes at about 34000 miles on my 2005 F-150. I read a thread about two months ago about this and went out in the garage and checked mine and the pads were almost gone. It must be correct that there is more rear brake bias then with the older trucks. The good part is that aside from cutting the rear rotors (which I didn't do, they weren't bad), the rear pads are very easy to replace and takes only a few minites a side to perform.