my 85 sierra blow the pvc valver out and i just replaced valve gasket. why am i getting to much pressure??????

valve seals may be bad

You don' t say how many miles or oil consumption but if its that high it could very well be blowby. Take a look at the plugs for oil foul signs and perfrom the test. You may need a new engine. If you do don't forget that you can often get a crate motor cheaper than hassling with rebuilding. I hope thats not what you need but it is a real possibility. Good luck