Im a F&B user when it comes to TB's, but the hesco tb would help, not sure how the spacer would really effect anything in f.i. i never seen a diff on my jeep when adding plates for other issues beneath my f&b
My gas mileage at 60 mph has improved from 16 mpg to 21 mpg. I think that's good for 30 x 9.5 R15 tires that are on the low end of acceptable street pressure.
New plugs, wires, cap and rotor didn't make much difference.
My latest tweaks were motorvac (similar idea as Seafoam), a new oxygen sensor, and a 205F thermostat. Since all 3 of those things were done at same time, I don't know how much gas mileage increase came from each mod.
I do know that on an LJ in the past I had a 205F stat put in and gained approx 2.5 mpg. So I assume that my XJ gained around 2.5 mpg from the 205F stat.
I think the other 2.5 mpg improvement is from the motorvac, the oxygen sensor, or both. Not sure.
Prior to replacing the oxygen sensor, it was tested by a Napa car care center. They told me the oxygen sensor was fine, but I insisted they replace it
Power at mid rpm has improved some too.
Warning: I often edit my posts a few times to get them complete, or to correct errors.