Upper Intake Manifold

I have a 2002 GT 3.8 with 61K on the engine. I had the upper and lower intake gaskets replaced about 10,000 miles ago. Now I am told that the upper is leaking again already. Could this be because they never replaced the actual intake and just the gaskets.

Yes, it is not as common on the 00-up's for the UIM to fail (it's usually just the gasket) but if let go too long, the coolant leak can erode the passages in the UIM. I personally wouldn't take the risk on reusing the OEM plenum with the aftermarket replacements being so cheap these days.

Is replacing the plenum and gasket a hard job. I would like to repair it myself instead if paying someone to do it again.

It is not hard to replace the gaskets for the UIM but it does take time. Check the maintenance section as there should be something there to instruct you on the proper procedure. However, I would still invest in a manual to make absolutely certain that you are doing the job correctly. Good Luck!