Please do not do "trial and error" with the SCT if you plan on running sustained or repeated high revs. The Coyote blocks weakness are the rod bolts and oil pump. Both of which do not like high rpm. There should be an adjustment for your tires, the 18" MT you discussed using in the SCT X4 programmer. Go to the tire size, select revs per mile, for the 18" tire its around 1200. Then see what rpms you go thru the traps with.