The engine just feels sluggish and drained w/ this stuff in there. It is not in my head either because I was very excited about this stuff and looking forward to the HTHS of 4.1 taking care of my engine in 90F days of A/C blasting and WOT's. But there is no denying the kess than enthusiastic nature of the revs as compared to the Pentosynth 5W-40 I had in there. I ordered some Motul E-Tech 0W-40. It's a little thinner but it's a real good basestock and additive package that should do the trick.