there's a couple things to keep in mind, not all tires/profiles are made the same, so one 30" tire on a standardly accepted wheel and backspacing setup, 16x7 4" backspace, may not find anything to rub, and another, will. (inserted photo) P-series AS street tire rubbed only with enough interference to polish the liner, but a 1/2" narrower, M/T profile tire rubbed hard enough you could feel it in the wheel. in terms of the suspension spacers, the KJ IFS has a tolerance of about 1" (enough for 2" of lift) before it starts doing progressively worse things in terms of coil/uca interference, leverage on balljoints, etc. there's not a lot of fudge room, that tolerance is closer to 0.9 than it is 1.1. Having the front IFS force a suspension extension cycle, under weight and inertia, with a suspension geometry length that's over 1" longer than it originally was designed for, is known to be a potentially very violent event. the angle at which the UCA and balljoint crosses with, for instance, a 1.5" extended geometry (3"RC lift) - is very close to the angle at which wine cork removers work at - and they've been known to "uncork" quite a few upper balljoints. Effective kj front ifs spacer use is common and successful at geometry increases of 3/8 to 3/4" - but the thicknesses of typical stand alone spacer lifts are above that - with a bit of hesitation/reservation, i'd be willing to admit that a 2" front spacer that's only 1" thick (not a spring preloader), is probably fine, it would be much better with 1/5" shaved off of it - it would be far less likely to cause the frequency of issues. Ive had folks who had beaten bushings to death, with balljoints you could move axially in the socket, by hand - not prybar - who stood there moments prior and swore they had no issues and didn't know what the big deal was. So i've never put much weight in the /just as good/no problems/ - humans deflect when faced with the potential for having made a sub optimal choice, if we all treat advice, and "reviews" as if our bad advice results for someone else, will literally come out of our own wallet - we'd all probably give better advice, or none at all. In terms of regearing, the CRD's second overdrive (0.67) will more than accommodate a swap from 3.73 to 4.10 in terms of highway cruise , regearing is the most cost effective, #1 performance increase someone can do to a vehicle, the torque increase at the wheels is about equivalent as installing a supercharger. I'd say its more crucial of an impact in regards to the 3.7, the 2.8TD makes adequate torque to grunt it and doesn't have a pronounced torque hole like the 3.7 does. The difference between 2000-2100 on the 3.7, and 2300-2400 is massive in terms of torque. Most 3.7 KJs with oversized tires and 42RLE's fall in a torque hole at highway speeds and effectively lose the effective use of overdrive below 75mph. 3.7s ability to maintain, or accelerate on any beyond minor grade below 2200 rpm's just doesn't exist, and it makes twice the torque at 2350 that it makes at 2100, that along with the FDR's effect on torque output, even the CRD can greatly benefit from it.