LAN=local area network, data stream. Several have wired in 6 speed tcm's and wired them up like you say, and made them work. Keep in mind though this method GREATLY limits what it can do. With a 6 speed tcm you would be greatly limited on gear selection unless you wired in the tapshifter(this only applies to lly/lbz, NOT lmm tcm's), but then you wouldn't have a gear display. You would be limited to only 1 trans mode(no tow/haul mode) unless you wire in something to trigger tow/haul. Without tow/haul you only get grade braking to 4th gear, and only get lockup at higher speeds. You could try and run a medium duty/kodiak tcm tune, but to my knowledge nobody has tried one with a swap. There's also alot of other things that will be different, hut the biggest will be how it shifts and the shift quality(or lack there of). With a mechanical injected engine you just don't have the repeatable power, smooth application of power, or defuel on shifts, and it WILL show in how it drives. I say this because several learned early on in the duramax power game that eliminating or even just reducing defuel could let a stock lb7 destroy even a built allison. There's alot more I could go into, but I'm trying to keep it brief.
No, 5 and 6 speeds will be about the same. And I would say it would shift more like a dump truck or something, just a solid push on you during a shift that gives you that jiggle on a shift. These transmissions were never really meant to go behind mechanical injected engines, but when they did there was a calibration setup to make it shift once the power started tapering off. Iirc the 6 speed was rated at 650 ft lbs of input torque with defuel, but only around 520 without defuel. The clutch to clutch allison trans does not like harsh shifts, there's just nothing to give, and harsh shifts normally mean tie ups(stuck in 2 gears at the same time). It's doable, but if it was mine, I would want a compatible tune to the style engine so you don't end up like one of the many that curse trying to swap an allison in. I hate saying it, but I would swap a torqueshift in long before I would an allison.
I've read that one before. Like I said earlier, you can get it to shift, but you lose alot of functionality. Without having access to the Allison DOC software, you're very limited as to what you can do. The calibration for the 3.9l with a 5 speed I'm sure can be gotten from Allison. Your biggest hurdle is it is in a light duty truck. An allison dealer can do ALOT for somebody with a medium duty truck, but because of the terms of the Allison sale from GM, light duty truck's are off limits to Allison dealers.
