It sounds like the ob and gp already have their doubts. So they may say they are supportive but when it comes to the time you will have so many restrictions placed on you that it will be really hard to get your vbac, like from the second you go into labour they will be timing you. That would be really hard circumstances to relax in and I personally would be find it hard to let go and succumb to the natural processes, which is where failure to progress can kick in.
I just cannot understand how your previous c/s has anything to do with having a big bub this time?? VBAC women can even birth breech bubs!It is just a birth and should have no impact on the decision to have a natural birth. Maybe Alan or someone could help with that, I just don't get it.