Less power after service? Non ZCP w/BM3

[M3Power22]

Hey guys,

I've been running BM3 Stage 1 since June and my butt-dyno-meter is telling me I'm pushing less power since my recent service at the dealer (oil change, spark plugs and cabin filter). Still have all the pops and burbles along with the GTS startup and custom HP/Torque gauges so I'm guessing the dealer didn't flash me back to stock. Despite some remnants of the tune, I re-flashed however the car still feels stock for the most part from a power perspective.

Not sure how accurate this is but I did a few runs and the HP meter didn't move past ~440 HP. Assuming this is correct, something seems wrong... I see a lot of chatter re: spark plug gaps etc. but I don't think all that's necessary for stage 1 besides my plugs were OEM to begin with.

Car is non-ZCP w/Dinan axle back exhaust and drop in filters...

Thoughts?