I'm running 11# with my 42's and they are at 81% DC. This is with 24 degrees of timing at WOT. Couple things to note, this is running a 50/50 mix of meth and water as well as being at sea level. Most likely with you running a 6.0 at 3800 ft and trying to run 12#, you would probably be safer upgrading to 60's. No reason why that shouldn't get you into the 12's.