RPM'son Ford F150

I have a 2012 Ford F150 supercrew with a 5L and 3.55/1 ratio. my question is this. I have had it for about a year and put about 12000 miles on it just driving around without pulling anything. I have become quite used to it driving in the 1500 - 2500 RPM range. In looking and reading some of the posts, I see people talking about driving and pulling all day long running at 2800 RPM's. Two big factors that I want to consider, gas mileage and wear and tear on the engine/drive train. Pulling a TT with a weight of about 6800lbs, I use a Equilizer distribution hitch, what is a safe/good range for me to run RPM's. On my drive home after picking it up, there were nice flat places where I did run in the 1500 range but going up some steep grades, also had to jump down into 3rd or 2nd and run about 3000. I may be asking too much, but I want the best of both worlds, the best gas mileage, and the least wear and tear on the truck.
thanks