Sorry to hear you are having problems with your Shark Navigator,I have one & I just luv mine,I have owned mine now for about a year problem free.I have filled my dust container way past the full mark & the suction remained the same as it was first cleaned out.I was just wondering did you ever check or clean out the top 21 cyclone chamber insert that goes into the top of the dirt container yet?I have found that when I clean out the 21 cyclone insert either by tapping on the side of a plastic garbage can ( every 3 months or sooner it states to clean that part out in the owner's manual ) or also I will wash the insert to clean all the dust & fine dirt out completely because sometimes tapping is not enought ( let dry for 24 hours before use ) when I am cleanning the main three filters.I have found when I do this full clean down of the dirt container with the cyclone chamber insert that the vacuum's suction restored to like it was new & the power head pulls itself back into the carpet,I have noticed with mine when these cyclones are full of dust & fine dirt that the powerhead does not pull down into the my carpet & does not fluff up the nap as it should.This is when I notice I should do the complete clean down of the dirt container & cyclone insert.I know one thing when I first purchased this vacuum & cleaned my home with it for the first time I had to clean the dirt container out about 6-8 times before the dirt was getting less coming back into the container.I thought my Old Bissell Healthy Home vacuum was doing a good job but my Navigator proved me wrong.Also the reason why your two upper filters are so dirty & clogged up & the lower is all clean & new is because the 21 cyclone chamber insert is doing it's job & the cyclones are full of dirt & need to be cleaned out.I hope this helps?Try it it just work with yours.Thanks
