The G670 and the G159 are two different tires and should not be grouped together. The G159 is a short haul truck tire that has had numerous failures when used on motorhomes in sustained high speed applications. So if you have G159 tires on your coach I would suggest that you replace them now. You can Google "Goodyear G159 recall" and learn of the problems with this tire.
The uneven tread wear on the G670 is caused by a design characteristic of the tire that is caused by uneven loading across the thread area according to most tire experts but you will probably never get Goodyear to admit it. So if you have G670 tires and you are getting the uneven wear that Richard described, just tolerate them until they get to be 7 years old and replace them with Michelin or Bridgestone tires to correct the problem.
Gerald