Thus far, the only significant difference that I've found between the NV3550 and the AX15 - or R151 or whatever Toyota calls it - is in the first gear ratio; the Toyota has a 4.31 and the 3550 has 4.01. That's a bit, but not a huge difference. I assume there's more to be learned.
The NV3350 is going to be at it's torque limit with a healthy 5.3. You are going to have to be nice to it or you will be scattering pieces all over the place. Adapting it to the 5.3 is easy. Less wiring than an auto too. Tell your programmer you are running a manual and you are good to go. Adapters are available from Novak and Advanced adapters.
When I posted up that info request I almost included "And before anyone tells me that I'm pushing the 3550, rest assured that I know it's at the limit of what it can take behind a 5.3..."
I know I'm going to have to be nice to it...which is not something I'm good at doing, to be perfectly honest. I know the 3550 is rated for around 300-ish, torque-wise...and that's pretty much what I'm attempting to get from the 5.3. Right now, I'm not sure whether it's smarter to spend the money on the adapter kits to bolt it to the 3550, or to look for a transmission that will settle into place nicely and handle the power. I'm concerned that if I swap trannies, I'll be into a t-case fitment issue.
I found that and was reading it just as you posted the link. I'm looking for more information on it right now.
I put in an e-mail request for additional information from them, since I didn't see ratios or torque ratings or anything like that.