In the GM VCM Editor Standard View, on the Engine Diagnostics [General] tab, and after selecting the Firing Order button, is there a problem indicated when each of the displayed Cylinder cells have been filled by individual alternative colors; Shades of Greens, a Yellow, a couple shades of Orange? Are these cylinders showing a Mis-Fire condition; colors other than green? In other words, should all cylinder cells be the same color; Green perhaps; in a perfect engine?