I believe your truck is an early 99 just like mine. You should not be able to open the wastegate by hand, it has a spring inside to hold it shut. A shut wastegate will not hurt anything, boost is regulated by fuel. Heck the 94-97 trucks don’t even have a wastegate. If you noticing signs of lower boost then it may be dust leaking by the factory filter and eating up your turbo impeller and engine compression. Take the intake hose off and visually inspect the impeller for good sharp corners and feel of it for too much play, also check inside the hoses for signs of dust trails. This is of course assuming that you haven’t thrashed the factory air box and put the DIY intake system on yet. (no info in your signature)