Tires

op wrote:
I have a 6 year old, 3/4 ton truck mainly used to pull our travel trailer. It only has 26,000 mile on it and tire tread is fine however age is starting to concern me. I have read it is recommended to replace tires at 6yrs due to age.

I found this in Michelin LT tire adds
Michelin Q&A

*** Q...What is the expected service life of tires?

A. While most tires will need replacement before they achieve 10 years, it is recommended that any tires in service 10 years or more from the date of manufacture, including spare tires, be replaced with new tires as a simple precaution even if such tires appear serviceable and even if they have not reached the legal wear limit.***
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I always pump a tire to its max sidewall when looking for surface checking or tread/sidewall cracking.
Tires that sit a lot as on a rv vehicle or dedicated to towing/hauling some type of rv or a utility trailer/etc a few time a year can develop internal issues from sitting for long periods.
Good reason tire expert recommend removing the tire off the wheels and inspected by a experience tire tech that knows what to look for.

Good used tires have a good resale market now.