what kind of fuel economy do the 8.1's with 3.73 get?

 

Not good

 

As I thought with my 454, put a bucket under the tail pipe. Maybe you could catch some of the gas that comes pouring out. Don't expect anything worth being happy about.

 

My buddy said his 8.1 Avalache got 15 MPG on the highway going from houston to San Antonio, TX. It is about 3 to 4 hour drive one way.

 

I have an 01 Sierra 2500HD Crew cab with the 8.1
In 3 1/2 years I have seen everything from 8-14 MPG. I have a heavy foot (tickets to back that up) but I probably average high 9s (9.8 or so) thats a mix of highway and city. Towing a 22' flat bed with 4 wheelers and dirtbikes it will get down in the 8s, all highway with the cruse set and no trailer I have seen 14.2.

 

Do you have any mods done to that beast or is it still all stock?

 

As far as performance mods no its all stock.

 

I agree with Brob04600; I have an 02 K2500 Suburban with the 8.1l; allison and 4:11 rear end. 10-14.5; though none of it makes too much sense. Around town it's 10-12; on the freeway loaded or unloaded (like a family trip) @ 70 I have seen 14.5; then again if I push it it's more like 10. Fortunately for me it hasn't dropped below that; then again I don't tow or have heavy loads. Mine's also very stock (about to change though)