Back in the day (early 80s) when Mobil1, the first popular, widely sold synthetic came out, I can remember those with pressure gauges being alarmed by the low pressure at idle. I was told it was caused by the more slippery nature of it. Also, around that time, cars started to use lower weight oils, 5-30 replacing the old faithful 10-30 or 40, or 20-50, all in the name of fuel mileage. What weight are you running? I ca remember my '72 Pinto (ok, stop laughing!) It burned oil so bad that I filled it with 50w oil, and two cans of STP. The blue haze subsided, but it had trouble getting over 50 MPH, and just felt very sluggish. Also, I once tried Arco Graphite oil, available for a while in the '70s, in my '63 Grand Prix with the 421 engine. It was so slippery that the car was noticeably quicker. But after a couple hundred miles, the graphite came out of suspension, and found the lifters. It never tapped before, and never stopped after. Of course, in the late '70s after the second 'energy crisis', Sunoco 260 was up over $.60/gal, so at about 4 MPG, I couldn't afford to drive it much, which is why I bought the aforementioned Pinto. At 20 MPG, the car paid for itself. Ahhh, those were the days!