The dream became a reality!

[fcatwo]

If you go new you might also want to look at some of the TV's that have gone to five speed transmissions. If I lived near RMR I'd have him use my 05 Tundra to drag his TM up those hills a couple of times to see if the more numerous gears in the lower range (top two gears in the Tundra 4 & 5 speed trans are essentially the same) in any way compensate for mines lack of power-train customizing.

[RockyMtnRay]

Originally Posted by Windbreaker

I don't mean to tell you your business but if you get a 4x4 and change the rearend gearing you will have to change the front end and the transmission also. It might be cheaper to spring for the new. I kinda looked into this some time back and went new.

True. Yes, both axles have to be regeared on a 4WD vehicle...and the front one is often substantially more expensive because (1) the differential is harder to get to and (2) the front axle usually uses CV joints due to the independent front suspension.

Not quite true. Transmission changes are minimal...the only change needed is to the drive for the speedometer. On older mechanical speedometers, that was simply done with a different speedometer drive gear..a $1.50 part. Newer electronic speedometers require a recalibrator device be wired into the circuit between the speed sensor on the transmission and the Engine/Gauge control unit. Wiring in the recalibrator is not difficult but recalibrators aren't cheap...usually around $200.

[RockyMtnRay]

Originally Posted by lwhansen

Thank you. Your experience is invaluable! Now I am convinced that I need the 6.0 or greater, that means getting a Suburban 2500, and since I want 4x4, it means a K2500. I think it is hard to be picky about axle ratio, when buying used. I have done a national wide search for K2500's, and have only found about 10 of them with low miles in my price range (cars.com, autotrader and eBay). Do you have any idea how much it costs to upgrade the axle to a 4.1? It is hard to find a place that can do the upgrade?

Lars

Welcome. Glad I was able to convince you of the need for the bigger engine to be truly happy when you regularly tow over high altitude mountain roads. A smaller engine (e.g. the 5.3L) that works "just fine" for a one time tow in Colorado or New Mexico will not be just fine for repeated towing over the high passes. I know first hand how fast the power limitations that were scarcely noticeable on the first trip become a huge source of unhappiness by even the 5th trip across the Continental Divide passes. And now that I've finally got very good power, more than once I've passed a loaded 1500 series Suburban that was clearly struggling to even hold 55 on a long high grade...and I had my trailer behind me and the Suburban did not have a trailer in tow. You would be not happy in the long run in New Mexico with a smaller engine.

Costs of regearing axles seem to vary quite a bit from locale to locale since much of the cost is labor. It really should only be done by a shop specializing in differentials and those are indeed pretty rare...but can be found if you do some searching in the phone book and talking to 4WD shops. Regearing is precision work (measurements to the 10,000th of an inch) and careful, meticulous shops are likely to be more expensive.

The shop that regeared my truck is about the best in my city (of around 400,000 people) and probably a bit above average in price. Their normal charge is $350 labor for the rear axle, $500 labor on the front axle. (I've heard of shops that charge as low as $250 on the rear, $300 on the front). In addition to the cost of labor, there's also the cost of the replacement ring & pinion gears (about $170 to $200 per axle) as well as the cost of "install kits" (shims, bearings, seals, etc.) which also are about $150 to $200 per axle. Add it all up and regearing both axles on a 4WD vehicle will range, depending on the exact shop and parts used, from around $1200 to $1900. It's a pretty sizable chunk of cash and makes it worthwhile to buy a vehicle with the desired axle ratio already installed...if you can find one.

[RockyMtnRay]

Originally Posted by fcatwo

If you go new you might also want to look at some of the TV's that have gone to five speed transmissions. If I lived near RMR I'd have him use my 05 Tundra to drag his TM up those hills a couple of times to see if the more numerous gears in the lower range (top two gears in the Tundra 4 & 5 speed trans are essentially the same) in any way compensate for mines lack of power-train customizing.

This would be a very interesting test...in part because the '05 Tundra not only has more gears but the ratios are a bit closer (there's a big jump from 3rd to 2nd on the '03s 4speed). But of equal importance, the '05s VVTI heads/dual intake runners almost completely flatten out the torque curve of the engine at RPMs over about 3500 (the '03 loses about 100 ft-lbs between 3500 and 5200 RPM). At 3400 RPM, the '05 has only about 5 ft-lbs more torque and below that the '03 engine actually has a bit more torque than the '05.

My engine mods have boosted torque mostly between 2500 and 4000 RPM; the axle regearing added 10% across the board. So...my '03 clearly will be able to stay in 3rd (1:1 ratio) much longer on a hill than an '05 can stay in 4th (1:1 ratio). Once the '05 does shiftdown to 3rd, it will easily stay with my '03...though at a much higher RPM. But once my '03 finally does have to shift down to 2nd, the '05 should be able to leave it behind while staying in 3rd.

But now that I have so much more available torque in 3rd (direct drive, 1:1), downshifts to 2nd have become fairly rare even on Colorado's steep and high mountain grades. So, to a degree, having more transmission gears isn't that big a deal if the engine has enough torque for towing on most grades to begin with. But once the downshifting has to happen, then more gears are better.

I've done no testing on this myself but have been told. Talking about GM (Suburban or Yucon XL) The 8100 has the alison trany just like the Duramax and you have a choice between 3.73 or 4.10 rearend. You cannot get an alison with a 6.0, and you can only get it with 4.10 rearend (talking stock of course). Bottom line the 6.0 gets it's torque from a lower geared rearend at the expense of higher rpms and lower fuel mpg. The 8100 will cost more at 1st however I've been told (please correct me if I've been told wrong) will have substantionaly more torque and with the 3.73 rearend some have told me they are getting better mpg than the 6.0 with a 4.10 rearend.