Have a 1998 Chevy 1500. Brakes work but not...

If this c1500 has rear drums, check to see if your wheel cylinders aren't leaking. If they are leaking this is your culprit. Happy hunting!!

If it's really hard and you cannot hear the booster making noise or it make alot of noise then I'd suggest getting a booster. Also MOST of the time the reason the booster goes bad is because of the master cylinder leaking fluid into the booster. If you take the master off and look into the booster and see fluid then replace both. If it has no fluid in it and the master looks good, then most likly the booster is the only problem!