Perhaps try disabling these two files as well (I didn't try the FSGU hot-fix):

AEC_KLAS.bgl found in \ORBX\FTX_VECTOR\FTX_VECTOR_AEC\scenery folder.

APT_KLAS.bgl found in \ORBX\FTX_VECTOR\FTX_VECTOR_APT\scenery folder.

I too had elevation issues with KBOS. Did a search for *bos*.bgl files in my World/Scenery folder and I found this: AFX_KBOS_flytampa_dummy.BGL Its last date modified on my system was 2009-11-21.

Renamed to AFX_KBOS_flytampa_dummy.BGL.OFF, reloaded and my elevation issues were gone.