Hey Lunarboy
I would agree with Ron but would suggest a. Ouple of tests to help the diagnosis. First try pumping the brake pedal a few times with the engine off, then hold the pbrake pedal down and start the engine. If the servo/booster is working correctly the pedal should sink a bit as the vacuum augments your foot pressure. If it doesn't it would suggest the servo and vacuum lines have an issue. Second test the vacuum valve on the end of the master cylinder on a 3500 or the valve on the remote servo if you have a four cylinder motor. It should hold a vacuum until the pedal is depressed. You can check this by unsnapping the smallcover on the top of the valve, careful when you do this as there's a srping and filter in there and you don't want to lose them. Once the covers off get someone to depress the pedal while the engines running. You should see the valve stem move in there and re-seat when the pedals released. In very rare circumstances the diaphram may fail in the air valve. If that happens it can stop the servo working. And that is an easy fix compared to pulling and rebuiling the servo. Having said that I think Rons got it on the money.
Good luck anyway,
Steven