engine stalls for no reason. either while driving or idling at a lite.just like shut off key but restarts with no problem.does not throw a trouble code.have run with fuel pressure gauge and holds steady psi.watched spark with led monitor but stalls with spark still fully available.may stall several times in 1 mile or may run for 1 week without a hint of trouble.replaced complete exhaust system 1 month ago over plugged catalytic convertor.i am a hd.mechanic but this has me stumped.is this vehicle just sticking out it's tounge and saying you know nothing?