What choose a reverse valve body?

The only stumbling block I have found in reverse valvebody (Slap Stick style floor shifter) was my friend and mechanic help I let take a run with my 10 sec Duster. He ran back to back 13 sec. The 2nd run I was closer and it sounded like he was leaving in 2nd gear. The 2-step button is on the shifter. Sure enough? When he let go of the button to launch the force set him back and he was pulling it into 2nd by still holding the shifter. Lol. Once corrected he still ran a couple 10th's slower. But was his first 10 sec pass.