Power Brake Booster Question

[SLS]

I971 Chevy C-10

Is there a way to 'test' a Power Brake Booster to see if it is functioning properly?

My Master Cylinder is fine (less than 200 miles on a new unit), and I have no leaks in the brake lines...and all wheels have been bled to the max...no air.

But my brakes, although they do stop the truck well, feel like like they are unassisted. The pedal does not do the old 'pump up' on startup only to fall flat after braking...and the pedal does not feel 'hard' either. I just feels like hydraulic brakes with no booster.

The vacuum line that comes in from the base of the carb is pulling vacuum (but I have not measured it).

Is there a quick way to check the booster (in place on the truck) to determine if it is not functioning correctly?

Thanks for any info! And Happy 4th of July everyone!