I am probably going to swap to a 4l80e soon and am wondering what gearing would be best to retain as much MPG as possible. I was looking at gearing charts and it seems a 3.73 will get me as close to stock as possible. I am wondering though, if I just leave in the 3.42's will I certainly drop MPG with the 4l80 if tuned properly?

And I am having the hardest time figuring out if my truck has 3.23's or 3.42's. Its a stock 04 5.3 ext cab 2wd silverado.

 

look in the glove box.. GU6 is 3.42s G80 is factory posi traction

 

gu5=3.23
gu6=3.42
gt4=3.73
gt5=4.10

 

Ok Ill look in the glove box on lunch. Any comments on gear choice?

 

only change in MPG i saw was around town and stop and go with the stock converter in the 80E. Its pretty loose compared to a stock 60E converter.
but if your worried about highway mileage your just goin to waste money in swapping gears.
I get 24mpg on the interstate doin 70, im still running stock 3.42s and 30.5" tire. 2000rpms - 70mph

Being a 2004 ECSB id say 3.42s,, but my dads 04 has 3.73s.

 

I lost about 1 mpg on the highway with the 4l80e, all factors equal in comparison wth the 60

 

About how much mpg did you lose around town? Would a stall, servo, shift kit, or tranny tunning help it around town do you think? I am still very new to autos and trying to learn as much as I can. They are the most complicated things I have come across in a while

 

I'm assuming you left in the stock 3.42's when you did the tranny swap? Or are you saying you re-geared the truck to semi match what the 60 was?

 

The 80e over drive is .75 and the 60E is .70

So i guess you could just say a 7% difference? to figure out what your mph/rpm might be.

 

id say about 2-3ish?

no servo in a 80E

Stall is gonna hurt the mileage around town since its "more loose"
Tuning will help the most.