Is the 'check engine' light on? When it 'loses power and shuts off' , is it like someone's popping the clutch on a manual trans. while holding the brake? If so ,have the TCM scanned for codes , as #2 said it may be a lock-up problem with the torque converter clutch SYSTEM. If the check engine light IS on you may want to have that diagnosed first. Post codes so we can help.