OK, wanted to give everyone an update on this.. We found the problem. Short of using a Leak Detection service ($$$), we decided that the air leak (suction side) HAD to be betwen the new skimmer and the pump - based on all the wisdom you all shared. Being that the original pipe was COPPER, and at the suggestion of a pool repair service, we decided that instead of spending $300+ just to do leak detection, we parlay that $$ into just abandoning the copper & replacing everyting with PVC .. After we dug up the trench all the way to the skimmer return, we found the air leak -- YEP, it was where the idiot contractor used a Compression fitting between the skimmer's PVC and the old copper pipe. It was WET when we dug it up. So anyway, we eliminated the copper, and properly sealed/connected new PVC to the Skimmer return port, and all is great. We now have PSI in the 13-14 range and no air coming out of the Returns. A strong skimmer now ... Thanks all for your advice.