Power loss at 4000

[John Larson]

0w40 oil?  Whyever would you do that?  It's NOT the appropriate oil for your
engine, and is likely to lead to serious wear problems.  20w50 is
appropriate and is what the engine was designed to use in moderate to hot
weather.  This could be a factor in premature cam wear and general bearing
problems, as well as cooling.  Whether or not the oil is part of this
problem, I can't say, but the life expectancy of your engine is compromised.
HTH, John