Okay got a good one for you...I made a trip to the other side of OKC yesterday (40 miles one way) and noticed that the K5 started to act funny (seemed to loose some power and act like something was binding). Got out and checked the front hubs, they were warm, not hot. Checked the t-case, again was warm, not hot. But the rear differential was hot to the touch (outside air temp was only 89). After it cooled down, drove it back home. Jacked it up and the rear seemed to be a little hard to turn so I let it cool down again. Checked the fluid level and it was normal. The only thing I can think is that the rear is about to come apart. I have Precision Gears 4.10 (thick) gears (3.07 carrier), stock gov locker, 12-bolt, synthetic gear lube, 33" tires. Also, after it warms up, there is a vibration/humm that starts at about 70 mph and the longer it runs, you can start to hear it in lower operating ranges and it becomes more pronounced. Swapped out driveshafts (I have a brand new, balanced spare) and it still did the same. Went to the lake today (took the Z-71) and after towing the boat and traveling, the rear end on it was only warm at best. My bet is the blasted rear is about to come apart. I know that the lower ratio's (numerically higher) will run a little hotter, but I think that this is a little to hot. Any opinions, I open to any and all suggestions. It's late and I'm heading off to bed, I'll check back in the am.