Originally Posted by RB04Av

If your truck is a regular 1500, it's the 8.6" 10-bolt. If it's a HD, or 2500 up, it's the 9.5" 14-bolt. Yes the 14-bolt refers to the bolts on the cover. Get up under it and look: the 10-bolt is more or less round, the 14-bolt looks lopsided and has square-looking parts. If the differential is a Gov-Lock, yes you should get rid of it and put in something better; TrueTrac or Eaton posi would probably be best. Yes of course the front gears MUST be changed at the same time, otherwise in 4WD, one end of the truck will always be trying to go at a different speed from the other, which is incredibly stressful on the entire drive train not to mention pretty bad for gas mileage. I would consider new rear axles at the same time if it's a C-clip rear.