Josh,
I have a slightly smaller pool but with the same pump and filter. Pool has been running since April 2015 and the first time I cleaned my filter was about 6 months later. I was worried because my pressure was not noticeable higher and just wanted to check what the filters looked like before winter got here. The filters were clearly dirty but nothing like the DE filters I've had in the past. I had very little plaster dust when my pool was new, so if you did, then Richard is probably right.
I'd be curious to know what your "clean" pressure was and what it is now, as well as at what pump speed you are taking the reading.
and.. if you have taken apart and cleaned a DE filter you should be right at home with your cartridge filter. It takes me a little longer to clean the individual cartridges, but I don't need quite as many cuss words as I needed to reassemble the DE grids.
Jim R