I've had for the most part good service from my 225 D ST tires. My 1st set were U.S made and except for a bent Lippert axle they never game me any issues. 2.5 years and approximately 10,000 miles.
2nd and current set are China made. I had one tire develop a hump on the top of the tread. I caught it in time and swapped it for the spare and continued on. That was last year and I'm still running the rest of the tires. 3 years and approximately 9-10,000 miles. I plan on running them for this summer as we don't have as many trips planned this summer, so I probably won't put much more than another 1000 miles on them.
At that point I think I'll replace them with the new Carlisle HD tire. Not so much because I don't have faith in the 225 ST Marathons but because the new Carlisle just looks like a better tire.
FWIW I'm way under on the combined tire load ratings and also keep my speeds under 65mph.
P.S, both tires were GY Marathons.