I Changed The Oil In My 5600 Yesterday. The Truck Has 70,500 Miles On It . To My Knowledge It Hasn't Ever Been Changed. I Took The Time To Remove The Pto Cover On Driverside And Wow ! What A Mess. The Fluid Looked Good When Draining But There Was Alot Cramp In The Bottom On The Magnet. It Took Me An Hour And About 10 Shop Rags To Remove All Of The Fluid And Metal From The Bottom. I Refilled It With The Pennzoil Syncromesh Fluid. A Word Of Advise, If You Intend To Change Your Fluid Take The Time To Do It Right! I Took A Oil Sample To See How Much Metal Was Actually Floating Around In There. ( Oil Samples Dont Cost Me Anything ) Now For My Question What Type Of Gear Lube Is Everyone Using In The Rearend? The Rearend Is Next Weekend Project.