Appreciate the continued work on this project. I noticed in the latest version (5.5.4) that transition levels are now based on pressure altitude as selected on the new Realism>Weather menus. Certainly makes it more realistic in some countries. Not in the US however, as QNE is always selected passing 18000 climbing and QNH is set passing FL180 on descent. (Abnormal QNH pressure can affect the lowest assignable FL but not for purposes of this game and rarely in real life.)
The fix for custom location files for US operations is to change the location text files labeling to reflect "transitionaltitude" as being 18000 instead of the present "transitionlevel" label used in older examples. Simply change "transitionlevel" to "transitionaltitude" = 18000 and altitude selections up to 18000 will be in QNH pressure altitude and voice communications will be accurate once again.
Excellent simulation!