8 1/4 axle specs??

I have an 8-1/4 in my Duster. I've already blown up an Auburn Sure-Grip, I've got a Dana Trac-Loc in there now and that one seems to be holding up pretty good. But the axles tubes are starting to twist, so sooner or later (hopefully later) this rear is gonna blow up and I'll have to replace it with an 8-3/4 or a 9".