If you spend some time on the HP tuners forum it's spelled out on how to do it. The vortec trucks control the tow/haul through the serial connection and BCM, but it's possible to wire in pin 71 on the blue connector that provides a momentary ground, and this will cause the PCM to cycle through the normal and performance modes of the trans maps. So you could have one set up for 'normal' driving with a comfy cruiser and lots of torque management and another that will slam shift with no torque management.... I just don't know how long a stock 4L60e would hold up to that
I still want to go back and wire in the a/c request module so that the pcm can control the idle when the compressor cycles. It works for now, but it's not very smooth in the transition. lot's of stuff still to do..