Definitely check the raw water pump impeller. I thought it was going to be a real PIA, but after removing the alternator and the cool fuel module, getting the pump off was easy. I had a couple of pieces of impeller missing so I had to go look for it.
You can take you engine serial number to
www.-go-fast.com and do a parts earch with pictures to get exploded diagrams of everything. The raw water path on my 2006 model was from the pump through the power steering fluid cooler on the back of the engine then to the heat exchanger and out each end of the heat exchanger into the elbows.
I'm assuming there's good raw water flow out the exhaust??? The issue could be the circulation of the fluid inside the block.