Truck shopping 04-07 model years. Advice please.

We have a 2006 GMC 1500 HD with a 3.73 that we bought two years ago. It pulls our trailer with no problem (5500 lbs dry), and has a high payload so I can load up the box as well. Everyday driving I average 16L/100 KM which is mostly highway not stop and go and towing 22L/100KM. I have gauges for trans temp as well as engine, oil pressure and voltage so I can keep an eye on things. The only issue I had was when my brakes gave out due to rotted lines, luckily I had the trailer brakes to stop us.