The grey bulks are a smidge better than the older blacks - but won't be up to bl power. The stock 3.3 or 2.5 structure lets the diff cases twist apart or open slightly pulling the R&P out of mesh - get grinding and eventually either pinion rips teeth off ring gear, or pinion looses some teeth. The 2.5 has 4 small 2mm screws holding the diff cup to the ring - another weak point, don't know if 3.3 upgraded this or not. Neither are shimmed stock, so some are diffs work/last longer than others. The stock spyders are another weak point and a good nitro diff will eventually have a spyder failure.

Nitro solution is alum diff cases, alum diff brace, alum diff cup with 3mm screws and good shim job. BL power/torque - something like UE diffs and alum bilks or flm hybrids with ofna style diff gears. Nitro upgrades will last longer than stock, but will be a problem eventually. UE (and alum bulks) or hybrids will fix it pretty much for good. Then you'll need drive axles and center drives - fortunately the 3.3 stuff seems to do pretty well here.