Too Heavy for E's Tires..either LRF/LRG or 17.5 tires

They choose the GAW to be 6750lb by the capacity of the tire...a 7k axle would need a 3500lb tire plus for safty...Dexter only manufactues 6k or 7k axles.. But either way when I travel state to state,on the highway I like to drive at 68mph(truck performs best at that speed 1900rpms) and then put road temps at90 to 120*..Good Year Marathons just BREAK apart...Montana 3400l should have come with F or G tires..So this week I took a chance....