Tire life and replacement

[RetiredGuy]

I'd be interested in feedback from other forum members about this:

My wife and I recently drove our Y2K Yukon XL to Florida, the total round trip was about 2800 miles. Our GMC is the 3/4 ton model, and the OEM tires are Firestone LT245/75R16E. The truck now has just over 35,000 original miles, and the tires still have half the tread, and the sidewalls have only tiny hairline cracks near the beads on the rear tires. There is no sign of dry rot or bulging, etc. I have always rotated the tires every 3000 miles, cleaned both sidewalls when removed from the truck, and applied Protect-All on the sidewalls each time. Total towing mileage has been about 5000 total, and I keep the truck garaged most of the time, as well as maintaining air pressure at 50-55 psi.

We were driving about 75-80 mph on the freeway, and I kept thinking about the many times I have read "replace your tires at 7 years, no matter how good they look". So, were we taking a risk using 10 year old tires for this trip? I felt reasonably safe as they are Load Range E, and have never been abused, run low on air, or had a pothole impact, etc.

Any advice? Thanks.