Sounds more like pad material buildup on the surface, rather than warped rotors. There is an ASTM (IIRC?) bedding procedure where you get the vehicle going 55-60 and basically do panic stops without triggering ABS down to about 5mph or so (no stopping!) then accelerate back up to speed and do it again about 10 times, and then you drive around for 10-15 minutes to let everything cool without ever stopping with the pads in contact. This gets the brakes and pads scorchingly hot, and is also useful for removing deposits from bad pads as well. My brother who’s been a mechanic for almost 25 years tipped me off to this trick when I thought my rotors had warped. I’ve done this procedure several times on my and friends’ vehicles, and only one of them wasn’t fixed by it, the pads were completely gone.