dont use kyosho gears as they strip faster, the material is too soft. they work and im using them right now but only becasue my LHS had a bunch for like 2 bucks so i bought them but they dont last as long.
get the aluminum diff cases and it should hold up, at least longer than stock.
is not that HPI is garbage like you said, is that they made this stuff to run with their engine not a 30 or 32 like we are doing. if you run such a big motor you better expect to have some carnage.