Deciphering My Rear End

[sdcfish]

Capev -

Interesting points you make. I am lucky to have found a set of 390's and didn't realize how rare they were.

I was thinking of going with the 410 gears too, but was told that I still wouldn't be happy. I am HOPING that the 390 gears will get me comfortable at 60-65 mph so I can drive to shows out of town etc......right now I am simply crusing at 45-50mph.

Here's the money question: Can I assume that by reducing my gear ratio from a 4.57 to a 3.90, that this difference of .67 which is about 14.6% lower than the way it is now, should I expect and count on my truck now cruising comfortably at 50 mph x 14.6% better? So now my comfortable cruising speed will be 57.3 mph? I guess I could make the rear tire a bit taller which would also help....right? I really want to be able to drive on the freeway at a mellow clip at 65 which would be nice. I guess I would need to add a 5 speed transmission in there which would give me an over all ratio of .75 (overdrive 5th gear rartio) x 3.90 which is 2.92....that sounds pretty darn good, but another $3000 for a NV4500 tranny installed.