Lots of variables. You dont mention hills. - - The OP is perceiving reduced power cutting grass going uphill with a bagger. How thick is the grass? How steep is the slope? Around this part of the country we have had good rain and growing conditions for grass. Turf tends to get thicker and take more power to cut as good conditions persist throughout the summer. This is the OPs 1st season with his
BX2200 and his basis for comparison is with a smaller lighter tractor mower that has almost the same HP. It
could be a fuel problem, but he has addressed that with fuel and filter changes. - It could be that the conditions just exceed the HP margin of the 2200 and he just needs to let up a little on the go pedal as he goes up the hill.