Whether or not you use 500k or open diff or locked diff will not have anything to do with whether or not it bogs, something changed from the time you tore it down and put it back together and I dont mean the diff. Something with your drivetrain or tune. Check to see that all components in your drivetrain spins freely. No brake binding ect.. if that checks out then your tune has changed. But I think your drive train is binding.

Good luck!!