(quoted from post at 22:26:15 06/28/13) Useful tire life on tires is right at 6 years. Any tire older than that being driven at highway speeds is a blowout waiting to happen. Tread depth, lack of weather checking, etc. has no bearing on that.
Wal-Mart gave you $40.00 more than you deserved.
If you are going to be driving that vehicle on the highway, do yourself a favor and replace ALL of the tires, before you kill yourself and/or someone else.
This tire was on the used motorhome that I recently bought. I knew the tires were old, and was planning of replacing them anyway, but this happened first. The tire was 10 yrs. old, and looked great, but was beyond it's useful life. I'm just glad that it was one of the rears and not one of the steering tires. Note the tread depth.