I have an '01 Silverado 2500HD with the 6.0 Vortec and 4L80E. I recently got HP Tuners and started playing with the tuning. I can't seem to get rid of this issue: If I'm going 40 or so and already in fourth gear and I need to pass or accelerate to merge, I floor it and get an immediate downshift, but only to third. It takes literally about five seconds until it downshifts again into second gear and actually starts pulling. Sometimes, that's fine, I only really need the one downshift, but other times I really need it to get up and go and that's when it really frustrates me. What can I do in the trans settings to get rid of this? Or could it be an issue in the valve body or something else with the hardware? Thanks!