Nice find, and the fact that the timing belt has been replaced is a BIG bonus. I towed our old trailer (25ft, 5500 lbs) with our old 2000 Tundra 4.7 for about 4 years and found the drivetrain to be very good for that era of truck. With the weight you're pulling, you'll be fine.
There are 2 repairs on those 4.7's that are common; one is the TPS (throttle position sensor) and another sensor on the throttle body, don't remember the name. The sensors run about $80-$100 and are not hard to replace yourself or for a shop to do. Other than that, the engine is pretty much bullet proof.
2016 6.7 CTD 2500 BIG HORN MEGA CAB
2013 Forest River 3001W Windjammer
Equilizer Hitch
Honda EU2000
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