Sorry but I am new to site. I use M1 in my 383 LT1 but in my 4.0L Jeep I have always ran Valvoline and now just switched to MaxLife. From what I have seen is Chevron the better Dino Oil to use in my 4.0L, I know you could pour sand and milk in the 4.0L and it would still run but I want to get the best life outta her but cant really afford or justify M1 in both cars. Seeing as how I drive a lot of highway miles in the Jeep and the 383 in the Formula gets oil changed very frequently, about every 2000 miles or 10-15 passes down the 1/4 mile. Thanks for any replies guys.