If you have any intention of keeping the tires, I would have them inspected by a heavy duty tire company by taking them off of the rims. That will give you piece of mind if they pass their visual test by looking inside the tire.
Personally, I wouldn't prefer Goodyear's as I had friends have trouble with them but yours are like new. That's why I would have them looked over really good and use them maybe for another year or so.
I have ordered new Michelin's using the FMCA program that should arrive at the end of this month replacing my current Michelin's with 57,700 miles. I'm just leaning on the 'safe' side replacing them at 7 yrs. as my date codes run from the 20th-42nd week of 2006.
Good luck and let us know what you decide.
MM.