I also put Valvoline Dexron VI and a Wix transmission filter in very early on. I converted the Cavalier to Valvoline Dex VI at 200,000 miles. I actually could feel the difference and it got synthetic transmission fluid the day it came home and every 25,000miles. I wish Valvoline made a full synthetic 15W-50 with their add pack but with an HTHS of 4.5-5.2, and a 100 C cSt of no more than 18, 40C cSt of no more than 130. I would put that in everything I own, tonight.
NAPA oil is made by Ashland, and is very similar to Valvoline oil - doesn't NAPA have a 15W-50 grade? I thought I read that somewhere.....
Valvoline has 4 or 5 different 50 grade oils. They have conventional, blend, MaxLife blend, racing, and full synthetic. Their full synthetic is a low SAPS oil with only 1910 calcium and no sodium an no magnesium. It is also very thick, as are all of their 50 grade oils.
I would love to see the Synpower add pack in an oil with the above specks.