Ok, Probably will have to have my tranny rebuilt. I have an 08 silverado vortex max 6.0l 4x4. Not sure what tranny I have as I can't find anything definitive. Its either a 4l60/4l65 or a 4l80/4l85 I believe.

Anyway, my truck has a 3.73 rear axle. Although, I do fine towing as I ALWAYS am in third gear when I'm towing, the OD is really high (2k rpms at 70mph) when I'm cruising. Since they are going to have the tranny apart anyway, I want to find out if I can have them swap out the OD gear for another gear that would reduce my rpms at highway speeds.

- I know that truck can run at highway speeds at lower rpms as the Silverado hybrid has a 3.08 rear end and has supper low rpms at highway speeds.

I'm looking to you guys first so when I ask the questions to the tranny guy, I don't get him to say it isn't possible just because he doesn't know. If I'm going to spend $2500 on a rebuild, I want it the way I want it and not what is easiest for the mechanic.

I did contact gear venders for the OD kit but since i have the "auto" mode on my 4x4, my drive line is not eligible for their product. Just a heads up for the discussion.
Thanks in advance,

Eric