I'd be looking into cooling modifications next, aftermarket HE, isolation kit, aspirated engines get heat soaked quickly, which is where you loss performance.

The dyno numbers seem pretty good, I've always been one to appreciate torque numbers, more so then whp.

Hard to pinpoint from the photo, but it certainly appears it's been leaking for awhile, and if not, that needs to be addressed soon. It could potentially be the well known breather cover leak.

Are you noticing your coolant tank reservoir level slowly dropping, that prompted them to check for a coolant leak? May want to look for potential issues with the intercooler.