Looking for some suggestions here.

Had my Energy Star 3.0 final last week, and all tests passed expect for the duct leakage to the outside.
The blower door passed at 1.18 @ 50 pac (was pleased with that), and everything else is fine.

The duct leakage, however, failed by nearly 400 cfm! The raters and I could not figure it out. We followed each duct and return checking for leaks but everything was sealed up very well that we could see. We even disconnected the hrv to make sure that was not taking in air, but it did not change the results much (about 15 cfm). We did find a couple things, but it reduced it by only about 20 cfm. The rater is stumped and thinks the duct install looks good. So we moved to the registers. We pulled a few of them and see gaps or areas around the duct boot to the floor connection where we think air is leaking. I plan on pulling all registers, sealing this area and then taping the duct boot over the subfloor to the finish floor, closing off these cracks completely. I will then install foam gaskets around the registers to make them a tight fit. The rater things this could be about 40+ cfm around these, with 12 registers.

The next step is to pressurize the ducts and smoke them. HVAC contractor will chase any leaks and seal them off at that time.

Does anyone have any other suggestions or things they have found to look for?