you replaced the entire assembly including the belt & it's inner items? ie: the belt frame (that sits inside the belt) & rollers inside belt & the complete outer casing ( cleaner section etc... )
if you did every item, have you tried putting a spirit level on the belt, then on the machine, just to check everything is level, because, say for example a heavy handed customer decided to lean on the tbu/fuser slide out unit it would bend down at the front i would imagine

this would cause the belt to drift to the front.
i have seen the plastic clip come off the charge rod inside the t'belt on a DP8070 which although older has pretty much the same t'belt system, this caused the charge rod to wear the outer frame down & the belt to drift.
but i'd seriously check the levelness side of things to start with.
Regards, Den.