What mpgs have you been getting? I'm steadily getting 23 to 23.5. I've hit 24mpg a few times but barely.
I've heard guys on 33x12.5's or even 35" tires knocking down 28 to 33mpg consistently in their TDI swapped Toyota pickups 4Runners & Tacomas.
Have you had your injectors professionally set up and balanced in the past 100,000 miles? Are you running a good intercooler setup, and not sucking hot under-hood air into your intake? That's always a big issue with a lot of swaps. A cold air ducted airbox is exponentially better than hot under hood air particularly in warmer weather.
Miles on engine? What does the compression test at per cylinder?
What turbo?
Custom tunes by highly reputable tuners are really the way to go, spec'd for your exact turbo and nozzle size as well as injector setup. Generic "staged" tunes are okay if thats the only option...
I'm trying to keep the lift on my 2 swap projects to a minimum, just enough to clear the tires desired, that's the only reason to ever lift a vehicle is for more tire clearance. The tires are the only real ground clearance altering mod.
Low center of gravity is better for handling on road and off road, and better for aerodynamics.
I'm also using an aluminum ftont skid plate off a 1992-1999 Chevy Suburban for an air deflector up front to help with aero, and have a big steel skid plate for the middle of the Samurai also. Wish it was aluminum but I'll see if I can ever find a huge piece of plate aluminum for cheap or in the scrap yard.
I read of a guy using truck plastic bedliner insert floor section material for a belly pan on his VW TDI car and increasing fuel economy several mpg with the mod... Aerodynamics is a huge part of mpg.
Also obviously skinnier tires help a ton. 255/75r17 Yokohama Geolandar G003 M/T, 235/85R16, 265/75R16, 255/85R16 Interco TrXus MT radials, 33x10.5R15, Kenda Klever 33x9.5R15 (amazing tires), heck I was even considering running 215/85R16 tires on my Samurai for street use just to get real skinny...