'07 Hemi, P0308 code, runs out great until cruising speeds 50-60 mph. Then the RPMs sporadically drop out and recover. P0308 code shows when this happens. Have changed plugs, coil, O2 sensors, Fuel & Air filter, Cam & Crank positioning sensors. Still the same, feel like I'm chasing my tail. Any thoughts?

 

Pull the valve cover, and have a look at the valve springs.