Print jobs have recently begun pulling many pages from the tray rather than just one. You've checked that the paper is the correct weight, that the tray is properly calibrated, and that the paper's edges are fanned, yet it still happens. What part of the printer will you MOST LIKELY need to replace?

If the pickup roller or separation pads get dusty or damaged, many pages may be picked up instead of just one. To fix the problem, either clean them or replace them. The fusing assembly is responsible for melting the toner on the paper, while the primary corona charges the drum. A paper tray is unlikely to need changing, and you've previously confirmed that it's properly adjusted.