I am replacing all the lifters and the intake manifold gaskets in my 1999 4.3 Vortec V6. The lifters started making alot of noise and when I pulled it apart they were either fully or semi collapsed due to sludge. I cleaned one out and the plunger now moves freely. Instead of cleaning all of them, I decided to buy some new ones. They are Mahle Clevite brand, made in USA and I can't compress the plungers by hand at all. Is thnis normal. I need to know 'cause I really need this motor back together! Thanks in advance!