As others have said, stay on top of the cooling system. This also includes an overlooked item, the fan clutch. Outside of the typical things like good, clean radiator, water pump, t-stat, hoses, etc., many overlook the condition of the fan clutch, which will show up as low speed overheating even when all the other items have been replaced.
210* is normal temp for most newer cars/truck and was done to meet emissions. Some will try to put in colder t-stats and such and find their mileage drops. This is because the computer thinks it is running cool and richens up the fuel mixture. Mileage goes down and you risk killing the catalitic converter.
I find if I am pulling a big grade or towing, it might come up to 215* and then the electric fan kicks in and it comes back down to 210*. I also find when pulling a big grade or towing, I put the tranny into 3rd gear and it helps keep it around 210*. Not a real noticable difference in gas mileage. On the highway, no trailer, I typically get about 21 mpg. Towing and using 3rd more often then not, I end up 18-19 mpg.
BTW, if you are running 245/75-16 on the stock 3.55 gears and the speedo sending unit gear wasn't changed for the larger tires, your mileage number may not be correct. I changed to 4.10 gears when I went to that size tire and changed the sending unit gear to the correct one for that gear ratio and tire size. Speedo is correctly reading and driveablity is exactly the same as when stock.
