Upgrade the transmission to an Alison.

[aabreton]

I would like to know if a 6 speed Alison transmission would fit in a 1999 GMC 2500 Suburban with the 6.5 td engine? Or one with more gear than the original 3 speed.

 

[Wreckinball67]

There's not enough room for an Allison without doing at least a bodylift. I saw one a long time ago done and I recall a body lift was needed. I'll try to find the article.

 

[MrMarty51]

There's not enough room for an Allison without doing at least a bodylift. I saw one a long time ago done and I recall a body lift was needed. I'll try to find the article.

That sounds interesting.
I read on QuadStar tuning site they have some kind of a package to install some kind of a 90 series transmission. I think that kit has more forward and taller road gears too.
Not sure whats all required to get one of those pumped into that Suburban.

 

[MrMarty51]

Welcome to the forum AA.

 

[Rockabillyrat]

The factory transmission is a 4 speed 4L80

Quadstar has a kit to install a 6L90. You could make a Allison work, but its overkill for a 6.5 in my opinion. The 4L80 is one of the best transmissions out there. I really don't see a need to upgrade from it. Guys are building them and putting them behind the Cummins.

 

[aabreton]

The factory transmission is a 4 speed 4L80

Quadstar has a kit to install a 6L90. You could make a Allison work, but its overkill for a 6.5 in my opinion. The 4L80 is one of the best transmissions out there. I really don't see a need to upgrade from it. Guys are building them and putting them behind the Cummins.

Thanks I don't know much about it, but when I'm towing my 10,000 lbs camper,it just feels like the rpm is really high.

 

[dbrannon79]

what are your rear end gears, tire size, and what speeds are you at when towing? most of these rigs usually run a set of 4.10 gears and will be a bit high on the rpms if trying to go 70+ mph. these trucks are more designed for towing at lower speeds like around 65 at most. anything over and your economy goes out the window.

there are a few things you can do, some will limit or lower your take off power but help achieve lower RPM overall, as well as a couple of options that are higher in cost, but you keep you low end power. it all depends on what your budget is and what you want to achieve.

 

[aabreton]

what are your rear end gears, tire size, and what speeds are you at when towing? most of these rigs usually run a set of 4.10 gears and will be a bit high on the rpms if trying to go 70+ mph. these trucks are more designed for towing at lower speeds like around 65 at most. anything over and your economy goes out the window.

there are a few things you can do, some will limit or lower your take off power but help achieve lower RPM overall, as well as a couple of options that are higher in cost, but you keep you low end power. it all depends on what your budget is and what you want to achieve.

Thank you, that makes good sense. I think I'll leave it alone, and ease up on the lead foot. I want to thank everyone for letting me join.

 

[THEFERMANATOR]

There's not enough room for an Allison without doing at least a bodylift. I saw one a long time ago done and I recall a body lift was needed. I'll try to find the article.

No, you do not need a body lift. I know my pics are gone, but I posted in my build thread here, back in 09, how I fit the Allison with a Duramax into my 95 Suburban with no body lift. I REALLY wished people would stop spreading this misinfo about needing a body lift to fit the Allison in a GMT400 platform truck.

Now that all said, you would be robbing an easy 20HP extra power from your 6.5l to turn the Allison than the 4l80e. You're turning a bunch of RPM's probably because of the amount of weight you're pulling, and you're out of power. The 6l90e would be a better fit IMO, but that is still a bunch of money to swap.