Your tires say 60 psi is the max inflation on the sidewall? What kind are they? Generally Load Range C tires are 50 PSI, D => 65 PSI, E => 80 PSI.
Generally if you're anywhere near the rated load, it's important to keep them inflated to that PSI. That's the condition under which the tire company "rated" the tire, and lower inflation causes more sidewall flex, which fatigues the sidewall and builds up more heat going down the road. Combine that with the very high pavement temps we've experience in Texas this year and you're getting the tire pretty hot.
When you're running "overkill" load ranges (significantly above the actual weight the tire is carrying) it's a bit of a different story. The tire itself has a stiffer sidewall, and some manufacturers have "derating" charts where they show the pressure to inflate an E rated tire for carrying D loads, e.g.
Il Carriaggio — 1975 Argosy 24 | Il Progetto — 1976 Argosy 28 Center Bath | WBCCI# 15566
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