Unlike an engine that produces contaminants (yup I put a centrifuge on my engine), other than moisture that may get in from warm up cool down, the trans contamination comes from mostly from wear of clutch packs.
The 545RFE has two filters, the inlet one in the bottom of the pan and the spin on one inside.
Use a good filter kit like Wix or NAPA and stick with ATF+4 you are doing the best you can do with out going all the way for a SunCoast/Transgo/ PML pan. If that is not good enough, Suncoast has 400 HP and 800 HP clutch packs that will fit into the 545RFE, but even with all of my mods and my Inmotion Stage II, I am only half way to 400HP and a quarter of the way to 800HP, so I will stick with what I have for now.