Since ST is doing a great job in audio compression you should rather expect the opposite - I had to turn it way down in order not to exceed 75 kHz.
Maybe it's just a stupid question, but... did you check the volume (MPX level) slider in FM-out in the Stereo Tool? If you pass the MPX signal from ST through VAC/Hi-Fi VB cable into MPX tool for example (you can try demo mode), what is the deviation displayed?
With MPX-tool in the chain at the very back-end, if you choose for example Unveil preset in ST, and set MPX level to -3dB, the MPX-tool should display exactly 100% (75 kHz), as it uses -3dB as a reference level by default. If you check that and all will be as it is supposed to (and sound right), then most probably the cause is something else than the ST processing itself. Note if you change MPX volume - the whole MPX-level changes and not the audio only (it affects all of its components proportionally - so lowering the MPX volume also lowers the pilot, rds and so on)
Also - check if you don't have another slider for ST specifically in the system audio mixer and whether it is not, by accident, turned down.