Sounds like its in LHM (limp home mode). Should display the check engine light for LHM. Read the codes to see if you have pending codes that may point you to a specific component. Nice thing with the V12s is you can swap parts side-side to find the failed component. Many times it ends up being the spark sensor on plug 6 or 12, but there are many parts that can cause it to go into LHM. Failed fuel pump, coil, cap/rotor, FPR, etc.