I just discovered a nice 3" gash in my Gander Mountain 100mph gore-tex rain gear. I bought it four years ago. It's on the left knee, and goes through the first layer of material. How do I patch it???

I patch pin holes in breathable waders with "ShoeGoo". For a gash like that you'll need a patch of some kind on the inside and seal the outside as well. 

I don't know how to patch gore-tex.  Call up gore-tex and see what they say.   If it is just a minor slice on the knee, I probably wouldn't worry about it.  The worse thing that could happen is that you knee might get a little wet.  I'd be tempted to go all Red Green on this issue and patch it with duct tape.

 

If the bibs were really dirty, I'd wait until after they were cleaned before I patch them.