The two things I would look at first would be the IMRC operation and hot air feeding into your intake system.
One of the ways that the IMRC (Intake Manifold Runner Control) fails is in an intermittant manner, particularly when hot.If the secondaries are not opening there will be a large loss of power above about 4000 RPM.
It is common knowledge that if you install an open element air intake system and allow it to suck underhood air, it will have lousy performance in hot weather. You need to find a way to get cold air up to it or a way to block the hot underhood air from reaching it. Some have made an underhood air dam with something as simple as a cut up trash can lid.
