Well thanks everyone for all the advice. I don't know how on earth I'm going to fit anything else in, but it's not too late for me to change anything if I've missed anything important ... I just designed this because they are places I've heard of from England.
This is how it stands roughly at the moment...
Arrive JFK Airport New York. 5 days in New York. Drive north for 2 days (travel agency want me to fly) to see Niagra and stay over weekend in Toronto. End up in Buffalo.
Fly Buffalo to Miami, pick another car up, and follow 10 day pre prepared tour round Florida inc. the everglades and beach resorts.
Fly to Dallas day before apostfest. Pick up another car. Can stay in Dallas up to 5 days.
Allowed 3 day drive to The Grand Canyon. 1 nights stay and then no hotels booked for the 3 weeks remaining to cover Las Vegas, San Francisco and LA and somwwhere in there a beer at Gumby's all at my own pace.