No it's not bull. Haven't you ever been skiing up in the mountains where you climb at least 2000'-6000'ft. during the drive up the hill? The car/truck you are driving will feel SOOO much slower. Way down on power. My foreman is getting ready to move to Colorado. I forgot which city, but it's up at like 8 or 9000'. They already bought the house up there and his wife has made the move. His wife's Honda SUV felt so much slower that she thought something was wrong with it! She was almost thinking about taking it into a shop.
Haven't you ever seen guys from Colorado post their times from a track that is at 4000' or 5000'? There times are always real slow compared to times others turn with similar mods down at 1000' or lower track. I run my Mustang at a track that is at 2700' above sea level. I've also ran my car at a track that is no longer around (Terminal Island, Brotherhood Raceway) that was right at sea level, basically on a man made island just several feet above the ocean water. I never made it there with my new motor. But on my stock motor with all of the normal bolt ons & 3.55 gears I was turning 14.2s on street radials. Same setup at the track in the high desert (2700') netted me several 14.7s. So yes, there is a difference.