Found a older air dog 100 new in box. Comes with the old fittings and roll of hose. 375 plus the ride. Should I take it or leave it? Also need to Change the rear end fluid in my 2001 what is the best to use? Dana 80 with limited slip.

Not bad on the price of the AirDog being I paid $520 for mine brand new. Remember you will not get a warranty with that AirDog being its sold 2nd hand.As for diff fluid I would just use 80w-90 gear lube with fricition modifier added. But if you plan on pulling alot and heavy I would consider 85w-140 instead. Like myself once this supply of 80w-90 goes I'll move up to 85w-140..

How about if youpull heavy but not alot? Less than 5k a year.

I'm cheating it with 80w-90 for now... But I keep a close eye on the fluid level and color and dump when it darken...

I looked at the FSM and it called for GL5 80w 90 unless the truck was going to be used for heavy dutyor trailer tow. For that it said GL5 75w 140 synthetic. I dont remember what the owner manual said. It also called out GL5 75w 140 synthetic for the front axle.I definately dont remember the front being callled out that way. I thought it called for 75w 90.