1997 Nissan Maxima Engine stalls after cruising

I have had the maxima for about 6 months, have had no problems with it so far, other then routine maintenance, and a service engine soon light which came on and went away after about 4 hours, likely the O2 sensor on its way out. My problem is after driving on the highway a cupple of times on the off ramp the car stalled, I thought I must have forgot to push in the clutch, and stalled it, but today I caught it for the third time, after driving in 4th at about 80km/h I came to a stop sign clutch in and car smoothly stalls, I am sure the transmission is disengageing so I don't think that is the problem, because as I said it happens smoothly it doesn't jerk what so ever. I clutch in and the car will start up fine and have no problems. This has happend 3 times now in the past 5 days, I live in canada outside temperature has been -20 C for the past days but it has been fine all winter in temperatures like this. I always use 91 octane, but recently used 91ocatane with up to 10% ethanol at a mcewan has station many thanks