i would take the flinch hax approach with iron head and zen headbutt.
trick room bronzong normally does pretty good with that, instead of payback and gyro-ball.
you only have 3 moves, fill the last slot with curse, and you could switch out overheat for return or frustration, and save yourself 252 evs, while losing a " back up " attack.
go for hammer arm instead of giga impact, you're getting neutral or not very effective, or even doesn't effect at all, damage on anything you hit. might as well use hammer arm, it'll boost your speed in t-room too! and it gives better coverage like i said before. life orb might work better, we're only talking a 20% loss, and... it's rampardos. you could afford a little less power for not being locked in to a move.