I don't drive a Chevy myself, but I do know plenty of places online where a Chevy Silverado driver can go for help with its power booster brakes.
Your first stop should be justanswer.com/chevy, a site dedicated to Chevy repair advice, where a similar question to yours has been answered by a professional mechanic.
If that isn't quite what you're looking for, you could always join an online Chevy or repair advice community, and ask for advice on power break boosters for a '98 Silverado.
Perhaps you want to go it alone, but you're missing the repair manual you need for the job?
If so, go to assets.gm.com/manuals/chevrolet, where you can find old Silverado manuals, or try calameo.com/books, an online collection of car manuals.
Finally, YouTube has a number of filmed repair tutorials, including this one for a breaks inspection of '98 Silverado, which might give you some ideas: