Power Brake Question

[Ron61]

I have been running power brakes since the car was built in 1996 and am having a problem which has been with me almost ever since then. I have tried everything but take it to a brake shop of which Redding has none that I trust.
The brakes work great and always have but when I have to get on them hard they will drag the engine down and actually kill it if I don't let off. Pedal stays where it should be, and I can lock the tires up. This has been a problem as I said above from day one. I have tried getting up to speed, putting it in neutral and costing as I applied the brakes. The more I applied them the more it drags the engine down. I think I have a Corvette power brake booster unit on there but can't find any numbers. It is a thin type to fit and clear under the fender where they go on a Classic Roadster type body.
Any suggestions as to what I could try? I don't have vacuum gauges and such, but the unit must be getting vacuum or I couldn't lock the brakes up. Pumping the pedal and holding it shows nothing as it will stay where I pump it up0 to until my leg tires of holding it.

Thanks,

Ron