So you are feeding the intercoolers & engine through the lower ?

I feed one huge sea strainer with the drives and a high speed pickup on the transom. Both engines draw from the single strainer. The setup has worked great since the boat was new in 06' until we switched drives.

I know this is an old post but I just went to IMCO SCX uppers with SC lowers on my 2007 38 Lightning with 600's and am having the same problem. Did enlarging the slot correct it?

I have a single 502 with whipple with an inter cooler with its own external pick up my engine is fresh water cooling with an ITS,SCX upper and sc 2inch shorty lower had the exact problem and turned out to be my pressure relief valve in my harden sea strainer. I eliminated the valve and are running less than 100 degrees with 20 pounds of water pressure when on plane (just a thought)