How do I know what part is bad

[vectorit]

Well, this last weekend I took my burb out for it's first time out on the road in a very long time. But noticed right away my breaks were not all that good, so I am worried that all this time sitting something went bad.
I had installed a new power booster and master cylinder maybe 8 years ago, and I am woried that over time the power booster went bad... Is there a way I can tell what part is not working 100 percent before I start taking things apart, and having to spend a lot of money on a new booster again? My gut is telling me that the booster has failed, but I am just hoping that there may be something else to look at.
Currently the break pedal is very hard, and the trucks breaks are not gripping well. Meening I couldn't stop in an emergency if I had to.
Before I pulled out of my drive way I pressed hard on the pedal to check if I had good break control, and one rear tire locked and made a little scid mark. But after doing that I can't seem to do it again, and now if you listen while the truck is rolling slow you can hear a clicking noise from that rear wheel.

Any comments on what I should look at first, and if there is a sure fire way to tell if a booster is bad other than a pedal test?

Thanks!