Can't burnout:(

I was with a few mopar guys last evening. Two of them tried doing a burnout with my car. They both said my front brakes are not holding, and there is an issue with the booster. I have always noticed the pedal get's hard right before I come to a complete stop. Almost like I loose my power assist. The pads were replaced last summer with raybestos. Rotors looked great so we left them on. Booster is probably original to the car but master cylinder is a few years old. Check valve is fine. While standing around the car they all said it sounds great with know missing, stuttering, and the rear rises up. Also said at one point the rear tires almost gave loose but my front brakes let off with the brake pedal as far down as possible.

We took a vacuum gauge to the booster while running in gear. One guy had the vacuum cap off the other port on the check valve. At idel in "D" it shows around 17psi. I then loaded it up trying to do a burnout. The gauge then showed around 5psi. I don't think it should be that low. The cam is only a 340 spec so nothing radical. Possibly my booster is going bad.

I was thinking about finding a large empty parking lot, disconnecting the booster hose from the intake and plugging it. Then trying to burnout. Would this be okay just to try? Or would I cause other brake issues? I guess I would basically have manual brakes.

I have another question though. I have had people tell me to start in "1" then powerbrake it to burnout and others say to start in "2" So what difference does it make? I thought it would be okay to start in "D"

Thanks again for all the feedback. Info is still appreciated.