I have a 472 hemi in a 67 R/T that runs cool in hot weather in traffic and down the road for what I say are short high speed runs. At 65 to 70 mph the temp will rise over 200 (slowly) if kept at the speed. Slow to 50-55 and the temp will go down. Alum rad with stock waterpump. I'm thinking a problem "could" be the lower hose collapsing at higher RPM. Does anyone use a non stock rigid or flex metal lower hose ?