I own a GMC Seirra Denali 2009. Recently I've tried to get an accurate reading for my AFR during full throttle on the dyno, but anytime I step on the pedal, the gearbox downshifts from 3rd to second and sometimes 1st.

I've tried using VCM suite controls to hold it on 3rd gear while selecting third gear on the shift lever, but it always down shift.