Something like this has kill switch problem writin all over it. But that can't be cause u already confirmed spark so that leads me to think it must be a fuel problem.
Maybe gas tank not venting properly and when bouncing around on the trailer pressure built up causing a vapor lock type scenario?
Have u replaced the fuel filter within the last 1000 miles?
Maybe u could have spark but the ecu is not telling the injectors to fire?
U could always try a couple drops of gas down each cylinder, give her a yank and see if it responds.
I've read that the kill switches (key, tether and stop switch) are hard wired but the throttle safety switch is software related. Maybe try wiggling that around