did you use a torque wrench to install the plugs? IIRC, the heat shield and the turbo/manifold didn't get in the way too much the last time I did plugs, and I think I used the torque wrench on all of them. You definitely don't want to over-torque these, but you also do need to get them tight enough.

Also, in case you weren't planning on it, you should just go ahead and replace all of the plugs at the same time.

I like to use a dab of anti-seize grease when I install plugs. Just don't get any on the tip or insulator of the plug, keep it on the threads.

Greg