Weird cruise control issue
 

Hello everyone. I have a 2001 F350 dually with manual trans. It has a DP tuner. When I am towing on the tow setting it will tow like it should for a little bit. I will start up a small hill, try to Accel to maintain speed and get nothing. The petal could be to the floor and get nothing which causes me to loose speed up a small hill. At the same time this is happening, if I push and hold the cruise on button (not the set/accel) button the truck will act regular, and this I mean the truck will pick up speed going up the hill like I was giving it fuel with the petal. Does anyone jave any ideas why the cruise on button would do this? Thanks a bunch.