TCAS max altitude strapped into the aircraft is the altitude above which the plane cannot achieve 1500 fpm climb for 30 seconds.
I was involved with original TCAS cert on the MD-80, and McDouglas left the altitude limit strap open, as it could hold 1500 fpm climb for 30 seconds at max cruise altitude.
Riding SLF on Jetblue A320, KLGB-KORD two weeks ago, the map display on the seatback tv showed us at 41,000 feet. I thought, Boy, Airbus bragging about Higher Faster Farther was right! Now you tell me 390 is max. The SLF altitude display is GPS derived, huh?
It showed 37.4 on the return Saturday.
GB