I assume that different year Dakotas spec out different weight reared gear lube. My 2001 manual on page 213 say all Dodge Truck axles contain fuel efficient SAE 75W-90 Multipurpose Type GL-5 gear Lubricant. On page 214 it does say you have to use friction additive if it has a limited slip. 75W-90 or 75W-140 does it really matter?