Getting around to changing all the fluids on the truck and changed out the rear diff fluid. If you have not bought a aftermarket diff cover I highly recommend mag hytech. This makes changing the fluid really easy and it holds more quarts of fact six quarts..I know sounds crazy but I checked it with the built in dipstick each time after four quarts. I know that in the past many people used factory gear oil with friction modifier but due to the crazy price I went with Valvoline 70w140. It is about half the price and it's a synthetic. To my understanding all synthetics have friction modifier in it. I chose not to put in any additional friction modifier. Has anyone else gone this route? Any issues?