I have had my PHP Phoenix since August, it was installed by Cody. No problems at all until yesterday. I had started truck and was letting it idle to worm up. I had switch set on 80DD, which is the #4 possition. Was showing my wife what was waht on the switch and when I went from #4 possition down to #3, which is towing, the engine cut out for just a fraction of a second

. Tried some of the others and there was no problem. But from #4 to #3 it cut out 5 out of ten times

. She had truck all day and in it again today so I have not got to try it "On-The-Fly". What could be going on?
Late 99 F350 7.3L