My 2000 Volvo 3.0 GS will run @150-160 degrees all day long at 3500 RPM or less. At 3500 and above the temp starts rising and at WOT move toward overtemp. When this happens I reduce the RPM and the temp falls quite rapidly back to the 150-160 level. I removed the thermostat and it obviously runs cold at RPM's less than 3500 but when I run @WOT the temp would creap up to 180-190. The engine has new wires,plugs,distributor cap,rotor,new circulating pump,new raw water pump and thermostat. Sounds like a blockage somewhere but don't know where to start.