Denny.....
My truck also has 48k miles on it and is in need of axle/transf. case lub change.
Decided to go with Ammsoil synthetic 75/90 (GL-5)in the differentials. Add 3 tubes of Mopar positraction additive if you have a Dana 80 with positrac.
I also have Amsoil synthetic ATF for the transfer case change.
Will stick with Shell Rotella-T in the engine as it is easier to obtain when traveling.
Good luck in your lubricating search.
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1998. 5; 24v,3500,4x4,SLT,QC,5 spd,3. 54LS, 4 whl. antilock, all options available when ordered, 18k lb. Reese full tilt 5th whl. hitch, oem full length diamond plate running boards, eyebrows & hood dam, bed edges,bedhooks; gray Rhinohide liner, Pac Brake, britebox,"deepdish"mats, matching topper shell, Sandstone(looks gray to me) & camel leather, stainless fender eyebrows, chrome(and road tar) exhaust turndown pipe; brush guard, SPA digital boost/egt(pre-turbo) gauge and pillar mount.
Lowered rear end 4" to set truck level.
See My Truck
1980, W200 Powerwagon, regular 4 door crewcab, 360 gas, auto, 68k original miles, 4 coats of Zeebart but losing ground to the saltwater anyway.
<A HREF="http://www.geocities.com/jr_fish_head/Orange_truck.jpg" TARGET=_blank>
The Powerwagon </A>
<A HREF="http://www.geocities.com/jr_fish_head/The_boat.jpg" TARGET=_blank>
My Boat </A>