I have an 04 2500 4 x 4 dodge with 5.9 Cummins. I've never changed the fluid out of my diff as it's always been out of sight out if mind. I've learned this is something I should have done some time ago. Anyway, first off, have I killed my gears? I don't drive the truck hard and I only occasional tow a 5k trailer. Second, what weight gl-5 synthetic gear oil am I supposed to use? I'd look it up in the owners manual but I've never had one. Also, is it as simple as draining with a mityvac and refilling or do I need to make a mess and remove the covers? As always, thanks for the helpful replies.