1st gen Towing with OD off

First about the truck: 04 V6 AC 4X4, Class III hitch/receiver, trans cooler.
Here is my question. I do not tow often with my truck (few times a year) and when I do it is usually U-Haul 6x12 cargo or utility trailer. The truck does fine towing, I can feel a trailer back there but the Taco just does the job. My question is more about highway cruising and the RPM I am putting on the V6. With OD off and if I go 65 (speed limit in TX for towing a trailer) my RPMs are well into the 3000-3250 range and not sure if mine is the only one that does this but the engine changes tone when it goes past 3K or so and sounds really loud-ish. For some small towing I do not see this as a problem as normally it is towing a few miles here and there, but what if I wanted to tow longer distance, say 200 miles each way on the highway. I can see with my ScanGauge that between 55-65 in OD/off the trans temp is staying nice and cool at 175 or so but how OK is it to run the engine at those kind of RPM for extended periods of time?
I know if I am to get serious about towing I should get a full size truck but for now the Tacoma does just fine. Thanks in advance.

--Dan