"I run straight Kendall 50 SAE and my pressures are stable",
Is your engine a gear pump?? That is insane to run that high of
oil viscosity, your roller lifters are probably starved for
oil. You want to run the lightest weight
oil which provides lubrication, even Roush recommends 10w30. New engines from GM and Ford run 5w20. Go ahead and install a 160F thermostat that will ensure your engine be worn out in about 3500 miles.