I also have a 3:90 rear, but I wanted to keep my low end grunt and so opted for a Gear Vendors O.D. It truly gives you the best of both worlds. I work the truck and tow a boat sometimes, so it was a no brainer.
My second choice would be to swap to a T-5.
The only way I would get a higher geared rear is if I didn't drive it much and just wanted to cruise or if I mostly drove on flat freeways.
P.S. I can drive it at 80 mph @ 2800rpm in 4th over. I can also split 3rd and 4th which is perfect for the sm420.
