Is there a way to preset your Mach before you get to 28,000?
Yes if you set the KIAS to the correct speed. Depends on aircraft.
Set your speeds to automatically change from airspeed to mach:
M .78: 293 kts
M .79: 296 kts
M .82: 309 kts
M .84: 316 kts
M .85: 320 kts
M .86: 323 kts
These are the machs for pretty much all commercial aircraft.
Thank you guys!