That sucks..I think I locked up in the hunter only once.
I've spent alot of time in it (at high wanted levels too) so you would think it would have happened to me since it happened to me before.
Were you doing anything special each time-- using rockets or anything--if you are firing alot this can tax the video...what was your wanted level
If it locks up again and you are trying to max out your money or something, try going into the audio set up and turning your sound effects down all the way and your music too-- I did this during my long vigilante run just because I was paranoid about it locking up and me wasting many hours-- also I tuned the radio to the "no station". I know it sucks playing like this but I just wanted to give the console a few less things to do.
Be sure to keep an eye on your wanted level and clear your stars if you get more then one star the next time you have to chase down the third car (bribe behind sunshine autos, one behind pay n spray in little haiti, and one just north of this one all reachable by air).
After you max your money--quit and save the game (don't risk losing your progress).
And above all--don't do anything stupid... don't land unless you have to and if you do, make sure you clear ALL your stars first, make sure you don't hover near the ground (they can pull you out) and the cops can show up on the airfield (although its rare), stay away from the water whenever possible-- be careful and take your time..there is no hurry in the Hunter.
Good luck.