Just remember, the 'relative compression test' is just that "relative",
I don't trust it much on a 6.4 as I had one that was missing pretty bad, all kinds of smoke, #8 was below -60 on power balance. Relative compression showed 0% varriance on all cylinders. Didn't quite sound right when cranking, so I thought I'd do a manual compression on it and would you believe that cylinder 8 was around 50 psi with all others on that bank around 320! Some 'relative' compression!
That was my first experience with a blowed up 6.4, and now it seems like a normal occurence for me!