Slick 60's

My C6 is getting tired and with 3:54 gears in my Dana ,RPM at 70 mph or so is a tad high. Rather than re-build ,is there a later OD that will handle a strong 460 with a minimum of pain and expense? Thanks

The later E4OD will do. Earlier ones were weak, but later ones (or rebuilt earlier ones) with improvements will handle even heavy towing, with sufficient cooling.
You will need an aftermarket electronic shift controller, though, as it is all computerized controlled shifting.
I considered going with an E4OD, but the transmission itself is much more expensive than a C-6, not to mention the computer control setup it requires.
For a little less outlay overall and a whole lot less frustration, I would go with a Gear Vendors add-on for your C6. These are extremely strong, are used in heavy duty applications such as RVs, and bolt onto the main case of your transmission by replacing the stock rear extension housing with an adapter for the Gear Vendors unit.
For now, I am using a 2.75 rear end gear behind my 460/C-6, but I am not doing any towing right now.
If I were to go for an OD, I would drop the rear end to a 3.50 or a 3.25, and put in a Gear Vendors unit.