Took me about 5 times to complete it. Lance is easy enough to kill. The KEY though (for me) was when coming back down to face Sonny and his thugs don't go for the office...
Come out on the top level (of main room) shoot a couple of the thugs from there... the cinematic plays, then just start lobbing grenades over the railing... takes about 5 grenades and you are done. Or Sonny is anyway....
I tried crankin my level wanted up before starting and it did help, but he blew past me right b4 last checkpoint! I will try dan da man's tire shooting strategy next...
I am gonna shoot that guy myself in the next mission like someone else said on here. Neurotic weirdo... Why do I need him anyway if I can outdrive him?!