1969 3/4 ton breaking 4x4 hubs - need help

[firefighter*17]

Hi every one! First post here, I have a 1969 chevy pickup 3/4 ton 4x4 stock 350 with a 4 speed manual tranny. The pickup either breaks the 4x4 warn hub or loosens up the hub bolts or breaks the bolts. Anyone come across this before? I use the truck to plow snow and I don't chain up the tires. The first time it happened I put high grade bolts back in, thread lock and torqued them down. Half hour into first snow storm I hear popping sound get out and look all bolts are loose and some missing. I replace, retighten and thread lock. I get back to plowing and same thing happens accept the hub breaks. I'm lost on this one and could use your advise.

Thanks!