GM 6L80 transmission in a '99?

[joe_too_crazy22]

Can a GM 6L80 transmission be swaped into a 99 nbs with a 5.3?

[joe_too_crazy22]

I guess, what I'm asking is: Has anyone done this? Did they use their stock ECM and reprogram, or go with another ECM?

I want better gas mileage, and I'm guessing if I could add 2 more gears I'd be golden since I swapped my axles to 4.10 gears already.

[transbuilderguy]

will not increase gas milage any the final drive on the 6l and the 4l is pretty much the same only difference is the first 2 gears that are lower. the 6l has a 4.02 ist gear where as the 4l has a 3.08 and the 6th gear in the 6l is a .67 and the 4th gear in the 4l is a .69 so there is virtually no difference in the gearing in overdrive.

[JadXtreme]

Along the same lines, can it be used in place of a 4L80E behind a 5.7? Can the blackbox pcm support the 6L80E?

[transbuilderguy]

no the 6l80e has its own TCM inside the trans it would require a pcm swap and alot of wiring its really more than its worth doing. you are looking at 4 gran for a trans to start with. plus electronics tuning and wiring and installation modifications to the crossmember.you have a 4l80e you already have a better trans in the first place.