I could be wrong on this, but I think this is only true for the 00-05's. In 06-07 the 3500 has a 2.84, and the HD (used in the V8) has 3.29...

 

wich means the hd trans will give a better gas milege the higher the number like the 2.93 will previde better lower rpm hence better gas milege. with the 3.29 has a better go than gas saver lower rpm 2.93. if you look at a rear end if you go from a 2.93 to 3.11 or 4.11 youll get higher rpm for the same mph but worse gas milege do to high rpm.

 

Good call, I didn't know that!

 

From what I've heard, the 3900 also has the 3.29 just like the V8. But the 3900 uses the non-HD version of the 4T65E. So apparently every engine offered in 06 had a slightly different version of the 4T65E.

3.5L= 2.84, non-HD
3.9L= 3.29, non-HD
5.3L= 3.29, HD

Like I said, I could be wrong, but this is what i've understood...

 

Strange that the lowest power engine also gets way lower gearing too- I wonder if they were just trying to maximize the mpg #'s or what?

 

I would assume that is exactly what GM was doing, they were going for max mpg's for corporate EPA estimates on fuel economy.

From what i've researched, this gearing (2.84) was also used in my mom's 2000 Bonneville 3.8L N/A...Why they used a taller gearing in the Bonneville over other N/A 3.8L's? Who the hell knows. LOL.

 

this is from the other forum im on. youll notice that it has an enhanced final drive of 3.29 but an effective final drive of 2.93. i dont know what the difference is between the two effective or enhanced but i definitely dont think that mine has 3.29s in it.

4T65E-HD Information

These are the upgrades that GM made to the MN7 version of the 4T65E-HD transmission to mate with the 5.3L LS4. Attached is the spec sheet for the MN7. One thing to add is that for the 2006 model year GM changed from Dexron V to Dexron VI fluid.
Quote:
- 258mm, RI 15 Torque Converter
- Enhanced Heavy Duty 3.29 Final Drive
- 2.93 Effective Final Drive
- Transmission case for transmission mounted starter
- Net-formed Input Sun Gear
- Ceramic bead Peened Final Drive Sun Gear
- Input/Reaction Carrier Assembly- Shot-peened Final Drive Sun shaft
- Upgraded Drive sprocket Thrust washers (new for high speed capability)

 

the reason why i think gm put a low gear in a bonivill is it is a crouser. and why not try to get good gas milege for longer trips. my uncles bonivill has the same engine and set up as your moms and he takes it every where for long trips. the thing is freakin comfy as well