13 MPG loaded? Much better then mine, but then again, I drive too fast. I get about 9-10 towing the Blazer, total weight around 16,500, and 14-16 empty. Thats with 3.73 and 265/75-17 tires. I am hoping that doing a 4" lift and 35's with the 3.73's will help with the mileage. We'll see.
I don't want to sound like your mother, but putting a 4" lift on your truck is going to significantly change the handling characteristics of a tow vehicle and possibly make it more dangerous on the road. No problem as a daily driver, but...as a tow vehicle? Just my $.02, as they say.
IMO (and I think the facts support it) any lift is going to adversely effect on-road handling to some extent. So will larger tires. Whether this is defined as a "problem" is, at least to some degree, a matter of personal judgement. That is why my truck sits exactly at factory specs for suspension geometry, but I opted for larger tires even though it marginally hurts brake performance and max power to the road as well as increasing side loads on the suspension. These drawbacks I considered within acceptable limits given my intended usage. Benefits were lower rpm at 80 on the highway, resulting in better mileage by keeping my rpms around 2k instead of 2.2k+ and better looks with more clearance for the occasional mild off-road excursion (like camp site, getting to trail head, whatever).
I'm just trying to be as tall as a stock "real" truck like the Fords and Dodges. Yes, I agree that the handling characteristics will change, but I will be using a quality lift, and a good gas shock, and plan to replace any worn suspension componets when I do the lift. I am looking for a rear sway bar from a 3/4 ton Suburban to help improve the handling. Also, I am sticking with 35's that have a higher load rating then the stock tires for my truck. I may end up with some airbags also, to aid in keeping the truck level. My trailer is a bit tall for a bumper pull, and this will help me actually get the tongue up where it should be. I would be worried if I hauled a large truck camper, or much more weight then I do. I am worried most about the gearing with 35's. I am hoping that the taller tires will keep the 6.5 happier for fuel mileage, without killing my towing power, and working the transmission harder.
