You'd probably get more relevant answers posting in the class A forum.
Six years for tires is not exactly out of line; most manufacturers advise a thorough inspection yearly after approximately seven years from date of manufacture (which means demounting the tires to inspect the insides as well as the outsides), and replacement in any case after maybe ten years. The exact times probably vary a bit.
For my motorhome, I generally shop mostly based on tire price. Any DOT approved tire should be safe to drive on (for its rated load), and it's unlikely that I'd ever wear out the tread on a motorhome tire except possibly as the result of suspension or alignment issues, so paying extra for superior tread life seems like a waste.