you can replace the gears. there are alot of companies that sell new gears for gmt400s. you could find a 14 bolt sf, very very very very 99.9% rare to find a legitimate 14ff 6 lug. Alot of our trucks (mine) came stock with a 14 sf. And if you're not doing some hardcore rock crawling or corr racing, a 14sf is all you'll need. and there are alot of 6 lugs versions of this axle.
BUT. if you get a 14sf with , say, 4.10s, you will need to get new gears installed for your front differential to match up with the gears in the back.
BUT. if you get a 14sf with , say, 4.10s, you will need to get new gears installed for your front differential to match up with the gears in the back.