rebuild replace? best option for rear diff.

99 ext cab, v6, 4x4, 2400,000 miles.

when i got the truck i noticed it has a clunking in the rear, thinking it was just a dry/bad ujoint i went ahead and got the truck. as i was fixing issues changing fluid i got to the rear diff which was full of a water/oil mix. noone told this guy he needed to change the fluids out every so often so when i drained the fluid it was full of fine metal shavings. i know there is slack/clearance in the gearset and its in pretty bad shape. now my option is to rebuild/replace. i have the tools and ability to rebuild the gearset if i can find a kit. i am pretty new to 4x4's and good parts sites. if i can find a good 3rd to drop in i would also do that but i havent found any yet.

using this site, http://www.tacomaterritory.com/wiki/index.php/Gear_Codes it looks like i should have a B06A, 8 inch ring, 3.91 ratio and 2 pinion open if im reading it right. i wouldnt mind upgrading if possible if it didnt cost an arm and a leg. just looking for opinions and different options. TIA