I was getting valve clatter because of incorrect back pressure, and thus changing the EGR valve should have helped, but it seems that it was more like I needed to do the EGR cleaning thing, and I did that today and it seems to have helped a ton!

So right now only problems that I can see:
-obdii does not have any power to it
-brake light is constantly on

We will see if valve clatter and back pressure issue is resolved, I have tried everything so far:
-tune up with new valve cover gaskets and plugs
-new timing belt/tensioner/bearings/water pump
-new EGR valve and gasket

I really hope this is not just a sticking lifter like so many 3.5's develop. I called the local shop that solely deals with engine removal and rebuilding/reinstallation and he said that Isuzu 3.5's are known for failed lifters.