OK I went back through and tightened all my hose clamps (was surprised I got a 1/2 turn or so out of the ones on the filter-these were tight 3 weeks ago). I let the filter run all day, it was at 25psi tonight, I opened the air valve and let it stay open for about a minute- the whole time water was coming out with some air too. I left it open til my psi dropped to 20, then simultaneously shut off the pump and pushed the control handle down so it was in between gears--this caused only a small belch out of the skimmer, backwash hose and return valve. It sounded like I got a belch from under the control handle though- is that normal when it's in between gears?
Oh, and the return valve does continue to push after the pump is off for about 10 seconds. I really appreciate all your help in tracking this down, I've only had sand filters before, but those only survive so long lol.