I can't remember if you are using MDI or Pump. And bear in mind I'm a T2 not using insulin. If you are on MDI, is your insulin expired/off? If pump, is there a problem with the set?
Other than the high BG, are you well? Have you a cold, flu, stomach bug? Are you experiencing stress at the moment? - While thos things can raise your BG, bringing them up to 300-450 does seem a big increase (depending on your normal levels).
I think that after a few days running that high it it time to see a Doctor. Have you checked for ketones?