Im not really sure which schools specifically want a GP letter but I would look at the websites of the schools that you are applying to just to double check and if you are worried you can always give admissions a call and I am sure they will let you know. UCSF just said they wanted a letter from a dentist whom you have volunteered with. I got an interview with them with a GP letter but I dont know if it will really make a difference if it comes from a GP or a specialist. Some people say that you should always try to get a letter from a GP instead of a specialist but I guess the best way to find out is to call the schools of interest.