Yep, you ain't going to get a much better ratio for a big truck. The only thing you may try is an over drive unit you mount before the rear-end. There's some postings already on here about them but there expensive. You might try rigging something up to. I'm putting a NP 205 transfer case in backwards in my driveline. Will give me a .5 over drive in high gear and about a .86 in 3rd. I can't say if it will actually work well though. I got the unit in the truck but haven't got my drive shafts cut or my rear-end back together. If you did this it would effectively drop your rear end to a 3.07. And as far as speeds...
With engine Running at 2900rpm in...
4th & OD my truck will run 98mph.
3rd & OD my truck will run 84.28mph
With Engine Running at 1750rpm in...
4th & OD my truck will run 59.1mph.
3rd & OD my truck will run 50.8mph
