Help selecting new filter for variflow pump

28k gallon IG,Pentair Variflow(up to 3HP), Hayward de4820 filter(48 sf). Pool and pump worked fine for 6 years, then started getting de back into pool. Been fighting this prob off and on for four years. Have read many posts and changed grids, manifold, orings, multiport, pump, tried to find suction leaks, added check valve, replaced jandy valve, at wits end. 2 years ago, purchased pentair variflow pump. Now I am wondering if I have too much pump for the filter. Maybe I had other problems that I have since corrected but the pump is just too strong. I have limited the output so it can't go to the max, but I am not sure if I limited it enough. Any ideas on how many rpms I should set as the max to keep from blowing out de powder? Also, I only have 1.5 inch piping. Should I get a bigger filter? and if so how big. Another de or change to sand? I am so tired of getting this de powder back in the pool. Please help if you feel inclined to.