My experience with the Goodyear G614 RST would tend to confirm that a major design change was made circa 2007. Our 2004 Mobile Suites 36RE3 came factory equipped with the G614s. In 2007, with the G614s 3 years old, we lost 2 tires to tread separations within a 3 month period (August & October); the 2nd failure did >$2500 damage to the 5th wheel. Goodyear replaced the first tire which did no appreciable damage when it failed. Goodyear replaced all remaining tires after the 2nd failure and paid to repair the damage to the 5th wheel.
The replacement G614s ran with no problems until July 2010 when I replaced them with 17.5" Michelin XTAs. Were they on the verge of failure at 3 years old like the first set? I don't know (in retrospect, based on the experience of others, I doubt it), but we were making a trip to Arizona in 100+ degF temperatures, and I didn't want to take a chance of any tire failures.
Based on my experience with the 2nd set of G614s, I don't have any problem recommending them to other 5th wheel owners.
Rusty