I am, but I just put them on in mid-May and have only towed for 260 miles. I'm at a state park where I am hosting for the summer.
In the little bit I have towed with the G614's vs the Marathon original tires, I would say my 5'er seems more stable and rides better. I also noted the tire temperature, I have a TPMS, did not increase as much as with the Marathons. My OEM wheels are rated for 110 psi.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof