can you go 100mph down a hill??

Why has the truck "never been in top gear"?

 

Right!!

 

He spec'd out a glider so he could run in direct for efficiency. It's got 2.64's under it IIRC.

 

So its not really "never"... I would assume he runs in high hole going down hill or when theres a 30 MPH tail wind. Otherwise, why not just spec it with 3.08 and run in final drive?

 

Running in direct eliminates geartrain losses, and he put an 18 in, instead of a direct 10, for better gear splits and a lower low. I forget the exact number, but I think speed at min. rpm in the big hole is around 90.