I think what you're talking about is a "kit" that many people sell (ATI, Art Carr, Turbo Action, Fairbanks, TCI, etc.) that uses a 2.74 low/first gear out of a Torqueflite 999 (modified 904, basically). I don't know that anybody makes a different ratio 2nd gear, though. If you look any of those aforementioned companies up, I betcha they all sell a "special low ratio" kit for a 727 that uses that gear. A lot of these companies like to make folks think it's something they've engineered, themselves, er something, but it's basically one guy's (year ago) project that was started years ago. I've seen, drag cars (kinda grew up around that stuff) in certain classes where you had to run specific types of transmissions. I.E. Ford Fun Weekend...for Street Outlaw, years ago, you HAD to run a Ford transmission (i.e. C4 or C6) and couldn't run a Powerglide, if you wanted to run an automatic. Guys figured out how to make the low gear set out of a Torqueflight 999 work in a C6 Ford transmission to give them that extra bit of grunt out of the hole/off the line, etc., etc.
I dunno. As most of us know, the 42RE is, I guess, a computer controlled or hybrid (partially computer controlled and partially hydraulically controlled) version of the A500, or an updated version of the A500, which is a transmission that is based of the "old" A904. The A500 shares many of the same internals as an A904, except is has an overdriven unit added to the @ss/back of it. The same is true of the A518/46RE/47RE (and maybe 48RE??? I know nothing about tht tranny), in that it shares a lot of internals with the "old" A727, or is basically derived from the 727, except it has an overdrive unit added onto the back of it, as well.
I'll call my old @ss (dad) this evening and ask him about some of this stuff. I grew up around his transmission shops. While I have a "fair" bit of knowledge and experience in mechanics (automatics, manuals, transfer cases, differentials, engines, fabbing up sheot, welding, etc.), I don't hold a candle to what he knows. If I knew half the stuff he's probably forgotten, I'd probably be twice as intelligent as I am today (I don't declare myself to be intelligent, by the way). Anyways, he knows a great deal more about what works with what, transplanting guts from this tranny to that tranny, etc., etc. I removed, reinstalled, and rebuilt trannies (as well as rear ends, engines, etc., etc.), pretty much all my life (or since I was probably 10 or so), but it was generally along the lines of rebuilding units that came out of daily driven customer cars, building T-5s, hot rod C4 Fords, hot rod AOD Fords (I was big into the 5.0/4.6 Mustang scene for a while from the age of 17 up through a few years ago), and sheot like that. Long story short...I'll call and see what he's got to say.
Sweet, it has been something I have wondered for a while. At one point in time I was actually considering swapping over to the 42RE from my 46RE to take advantage of the lower 1st gear, but wasn't sure how durable the tranny would be since it would be in my tow vehicle.
The 42RE and RH seems to work fairly well in the V8 Grand Cherokees, but they aren't rated or intended to tow as much as even a 1/2 ton Ram either.
If this 1st gear swap is a viable option, I'll definitely do it when my tranny needs a rebuild.
I'll try to stay on point. I would think my first response is about all the more I can offer in response to your question. A Torqueflite 999 first gear ratio is like 2.74:1, which is a bit deeper than a 904 or 727's first gear, but I don't know about the second gear changes. Like I said, most of this stuff was "developed," for lack of better words, by the drag racing community. You might call or check out Performance Automatic, or one of the companies I mentioned earlier.
Not to continue the hijack, but DO NOT go to a 42RE!!!! They will not last in the back of a Ram at all!!!!!! I have a 46RE and a 42RE and there is no comparison.
As mentioned, they share parts with the old A500 stuff. The 46RE is based of the A518. They have totally different sized internals and smaller drums for the clutch packs.
If you want a beefed 46RE/A518, then you need to get the larger drums/clutch packs from a 47+RE.
Many, many of the internal parts and designs are identical. If you get a shift kit from Transgo, it universally fits all the 900,904,500,518,6** 46,47,48RE/RH,42RE, etc. But the other parts like the drums are NOT interchangeable between the smaller 900/500 (42RE) series and the larger 500/600 (46+RE)type series.
Well, before anybody gets confused, let's clarify the "series" of transmissions and what other transmissions they "relate" to...
"A600" series were/are front drive Chrysler trannies (don't know what the current monikers for them are)
"500" series were/are rear drive Chryslers, replaced by 40-something RH/RE monikers
The A500 is an overdriven (4-speed), hydraulically controlled automatic placed in Jeep Grand Cherokees, Dakotas, and behind V6 powered vans and 1/2-ton 2wd Rams (did I miss anything?) and is/was based off the "A900" series 3-speed, non-overdriven automatics produced in the '60s, '70s and '80s. The A904 was used in a slew of Chrysler products, including cars, trucks, vans, etc., with slant 6s, small V8s, and AMC/Jeep products with 258 6-cylinders and some V8s. The A999 was used in other various Jeeps with 6 cylinders and V8s, and the A999 has the deeper 2.74 first gear in it. The "A500" designation was replaced by "42RH" (still hydraulically controlled), which has been replaced by an updated hybrid (partly still hydraulically controlled but mostly electronically, or computer, controlled) "42RE." Hence the "E" on the latter's designation, referencing electronically controlled.
The A518 is an overdriven (4-speed), hydraulically controlled automatic placed in V8 Ram vans and trucks (from roughly '92-'96) and is based off the A727 3-speed automatic that Chrysler put behind larger V8s in cars and in trucks from the '60s through the early '90s. A A518 designation was dropped in favor of "46RH," at some point, and the "udpated" version of the 46RH is the hybrid (see above) 46RE and 47RE (47RE used, primarily, behind the 8.0 liter V10 and Cummins diesel), and I would guess the 48RE is just another modified/"fortified" version of the same design.
The "old" 3-speed Chryslers (A904 or A727), Fords (C4 or C6), and GMs (Hydramatic 350 or 400), are, for the most part, tough transmissions and will take some abuse. They all can be built to withstand quite a bit of power (especially the bigger units of each manufacturer...A727, C6, 400), but for whatever reason, their modern-day, overdriven derivations haven't proven themselves to be nearly as tough, nor durable, on whole.