Stalling With Dp-Tuner

I have a 2002 7.3 all stock except for Dp-Tuner. The other day I pulled a boat to the river and it did fine all of the way there. When I backed the trailer down the ramp I put the truck in park, but hit the DP switch and the truck stalled and shut off. So I unplugged the switch and pluggged it in. So on the way home it still didn't act right. The truck was stalling every time when it shifted from 1st to 2nd. It was almost like a studder. When I got home it barely had enough power to pull up a steep drive-way. I don't think it's a loose connection because I moved the switch around checking for a loose wire. Anybody have any idea what it could be?