Sorry for the problems! I bought a 5 HH Sub a couple of weeks ago out of curiosity and, it definitely holds it's own. I did my usual 2 day setup, checking every screw (especially the bridge & neck) to include new strings, as usual. It runs right in the pack with my big dogs. Plenty of output! I was surprised at what I heard. I'm gigging it for the next 3 nights. I have no qualms about it whatsoever. Make sure you check your blend.
Tap the pickup with a metal object to make sure both sides are working? Adjust accordingly. If you don't have a solution, can you return it for another one slating output issues? Maybe I got a fluke, dunno but, I'm satisfied.