Thanks Joseph.
Willy at Wizard auto in Albuquerque is fixing me up with a new main shaft and fifth gear set and since it's apart at over 180k an overhaul on the NV4500 to boot and all for a good price.
A Note to all you folks out there that lose fifth gear: Just have the new main shaft put in immediately and save the hassle of thinking it's fixed and having to repeat the hassle.
I first lost fifth gear on this trip in Vegas and had Drivetrain.com (nice folks) put in a new nut with all the cool upgrades (staked, loc-tite, etc) but the nut still fell off after only about 400 miles pulling my fiver. It's the mainshaft and fifth gear plus an inadaquate nut design plus the harmonics of pulling a load in fifth gear while your rpms are below 1500 that are all factors in the problem.
My research for a better solution led me to quad4x4.com out of Montana that has developed a better designed mainshaft and fifth gear and nut but they are having trouble with their manufacturers and the kits are not available right now. They are hoping by the end of summer 2005 they will have a better supply so Willy is putting on the Piers version instead.
Thanks to Joseph and the TDR.
-Rusty