when air gets thinner( lesser air density= lesser air mass)due to elevation, the engine will theoritically has lesser compression load thus letting the engine revs higher than normal( of course it's because the engine has been tuned at different elevation of sea level; i.e; the engine air/fuel tuning would be different if tuned at different level above the sea level)
But, it's only a slight change because the ECU will normally had tolerances setted for air with different densities,pressures,temps etc.
The turbo system will have the same concept too, i.e to get 1 bar of boost in genting, the turbo has to spool faster than it does in Klang valley.
This is theoritical opinions.
Thnaks and enjoy ur revs!!!