http://www.gearvendors.com/cg2wdt.html theres some great overdrives for Muncies and Borg-Warners.
I know of one person (F-150 Lightning) who put a Gear Vendors Overdrive unit behind his E4OD and had 3.73 gears in the back. When he was going to Lightningfest in Kansas in Sept, he was cruising at 70-75 most of the way, and his engine was practically idling at about 1700RPM. After a couple years I think the money you save on gas would easily pay for it.
Drew