Overheating issues on a 95 prostar

[jdredfield]

I have a 95 prostar 205 with about 300 hours on it and I have never had a problem with it. I ran it in a river last week and could've picked up some trash but as I run it for a while at speed the temperature slowly rises until it gets close to 220 or 230 degrees and then the engine will shut down. I have tried to flush it and I've looked at the impeller and I'm putting in a new 143 degree thermostat. Where else should I look for trash? What is the canister that is inline on the water pickup hose? It has a couple of oil looking lines coming off of it. Should I pull that? The original invoice lists the engine at 275 TBI 1:1. I am assuming I have a plain jane chevy 350. Is that correct?