Gypsy, it takes time, but it's not that hard, just beat the snot out of it, crank it up, floor it, repeat. I think i spent about an hour on it. Then i drove it with the flange open up a nice incline and checked it a few times.
Joe, as a crd owner with 3.73 gearing (stock) and 32 inch rubber, you dont want, or need, to re gear. even if your towing, your going to be out of od anyway so your looking at what,
Max tq is at ~ 1800 rpm , witch imho is to low of a speed to keep trans pump pressure high, i think it does better at around 1900 to 2200 (towing)
3 gear at 2200 rpm is 56 MPH (locked) your going to be like 2300 unlocked
4 gear at 1900 rpm is 65 MPH <-- your pulling a 4% grade @ 22 psi and 4400lb <-- this is PERFECT
5th is 1700 rpm at 65 mph this is imho to low to tow anything above 16 psi or so (i get a load of shudder here) <-- this is great economy, if terrain allows
Also might i add that 2100 rpm in FOURTH and locked is SEVENTY MPH
You can easily hold high grades at this rpm and loaded.
1900 rpm with near stock rubber (29.3) is 66 mph in fifth.
Unloaded, i cruise up ridiculous grades in top gear at 65 at 1700 rpm. It's excellent.
I think 3.73 is great. And when i said third gear, I mean third prime.
Shoes are funny because their size changes based on load and speed, and different rubber has different characteristics. Also temp has an effect on it. It's not usually significant were talking 40 rpm difference (for us) between mfg with the same diameter max
check out this
Handy Calculator
I already have the proper ratios and so forth plugged in, however 3rd is third down and fourth is third prime fifth is fourth sixth is fifth.
As noted it's not entierly accurate, bfg says thier 235/85/r16's in km2's are exactly 32 inches, however i am exactly 1709 at 65 in fifth and this calculator says otherwise. I have also had other calculators show it as 1750 rpm. It's not, it's 1709. This calculator attempts to fix some of the problems with these types of mathmatics but it over corrects imho.
bottom line is 4.1 gets you 65 at 2k rpm in fifth (really sixth), 3.73 does the same in FOURTH (really fifth) the only thing you gain is interesting characteristics in 1-3rd (really 1-4) gear, easier burn outs, and crappy unladen economy.
Now, if your crd runs like crap, i don't know, when i bought mine there's no way it would hold gears with stock rubber on things it destroys now. via inmotion II and no muffler/empty cat, etc etc.