cruise set at 78 yielded 23 mpg.
Good questions. Calculated mileage makes a big difference. The quality of diesel seems to make a difference also.Dimensionally the tires are the same exact size though? So likely the speedo isn't off. You hand crunch your mileage every tank?
I wonder how much the new wheels weigh. The stock wheels weigh around 31lbs.. wonder if your new ones are even heavier, which could def. hurt mpg.
I think the idea of a 'leadfoot' varies greatly from one to the next though.. so that isn't a helpful description for me
I thought the wheel weight only hurt during acceleration from stand still. Tire pressure could also be an issue. Confirm they are actually at 35 psi with an external source.
One of my employees told me he wasn't a lead foot either, but was only getting 17 mpg in his Cherokee (not Grand). I rode with him. He is correct. He wasn't a lead foot, but mph varied 5 mph slow down, speed up, slow down speed up. I told him to start using the cruise control to see what that would net. Sure enough that fixed his mpg. At least with Matthew, he states he had the cruise set.
I would change the oil, check the air filter and possibly the fuel filter. Something is forcing your T'reg to work harder then it has to. I also know that my Exec gets 29 mpg with mostly "highway" driving. Interstate seems to do about the same if I keep it under 75. I always have my MPG per tank displayed so when it starts to drop then I know I am doing something wrong or need to change something.