The normal range for the 6.0l engine when towing is usually around 190 to 212,but it all depends on ho w heavy the load is and what the ambient temperature is,it is possible to run up to 230* and not have a problem.
Thanks. The oil cooler was changed about a month prior to the thermostat and head gaskets, due to an oil overheat problem. I am leaving Las Vegas on Monday, headed to the Mojave Desert in CA. That should be a good test.