Bad Right Rear tire wear, Limited Slip Diff?
 

I have a 1998 Chevrolet Silverado 1500 5.7 ltr 4 Wheel Drive 3 door pickup with 156,000 miles, great truck. Last 20,000 miles Right Read tire has worn smooth while other 3 are fine. These are Michelin with 48,000 miles on them.

I cannot figure what is Problem. Brakes are good, no dragging. I thought this had a Limited Slip Differential but rear end code is G14, not G80. What is G14, how do I find out?? I don't know how to check this, what to look for. Our GM dealer closed about 2 years ago, I am on my own. Other than that this has been a great car. I have a coffee farm and this is my daily driver, some 4 wheel drive, some highway miles. Anyone ever had this problen?