Heard that it is a good idea to change the rear -end oil to a synthetic?Better mileage, longer life. What weight in a synthetic would be the best to use, say in Calif. and towing? Is Torco the way to go, and also, do you have to pull loose the differential cover to drain out the old oil, or can you use a "sucker" pump, which , of course, wouldn't get all the old oil out. Can you mix a little of the original oil with the synthetic without hurting anything?? I have an 01 with 6k on it. Thanx for your input.