Jep...does, again, sound like brake fade.
I guess the first thing I'd try is bleeding the brakes and wiping the rotors down with solvent to make sure they are contaminant free. While you're under there, take a peek at the pads and see if there's anything unusual looking about them.
If it still behaves the same after that, I'd change the pads or bring it some a tech.
1985 300SD - 'Grace' (198K mi.)
2010 Honda Fit Sport
2013 Honda Accord Sport
1996 Lexus LS400 (Retired)
1995 Ford Contour SE (Retired)
1976 Porsche 914 (Sold)
1972 Datsun 240Z (RIP)