I have C1900 that stops suddenly, usually in the first 1/4 mile of a 30 min. workout. It stops abruptly and I step up on the sides for about 30 seconds and then resume the rest of the workout with no more issues. Today it stopped twice in the first 1/4 mi. then no more issues. I have replaced the drive belt, the walking belt and the Mylar cover on the walking board. I check the walking belt alignment and tightness all the time and it is within recommended specs. I also notice speed fluctuations at times but not enough to show up on the digital readout. My weighs about 100 pounds less than me and it never misses a beat for her. I weigh 240 lb. I hate to start throwing expensive parts at it without knowing for sure what the problem is. Any help would be appreciated.