I did this today. And when I switched to gasoline the engine braking vanished - or if it was present, was much diminished compared to what it was on LPG. Only had one shot at it (but will try again when I'm out and about again) but there's definitely an aspect that is DFCO related in all of this.
(FWIW, my default actuator setting (where most driving is done) is 155. Think of this as a main jet in a carb in that it controls how much fuel (LPG as vapour in this case) can pass. My DFCO actuator setting is 40. So about 25% of what it's normally at. Set at 80 the truck runs away and needs a lot of braking to slow it (and check its speed on down-hills). Set at 30 it gets pretty horrible to drive - the transition between on and off throttle is abrupt and jerky. What isn't obvious is where it gets air from when the throttle plate is closed. I can only guess the IAC valve permits/admits it).
