I bought this unit new in 2009. Model #927236 Ser# 07060076 Have had this issue since then. Mower starts right up and runs beautifully. Sometimes it stutters and stalls after running for as little as 15 minutes. Sometimes it won't stall for 8 hours or more. I've had 1. the tanks flushed out 2. coils replaced 3. new fuel filter and lines 4. new carburator 5. new fuel pump. 6. new fuel pump relay. 7. replaced all controll panel relays. 8. replaced safety interlock circuit board. 9. bypassed seat safety switch. Sometimes the motor begins to stutter and you can pull back the controls and put them in park and the machine will recover. Most times, however, it stalls. I have to leave it sit for about 3 to 5 minutes until I can restart it. Upon start, it gives off a little smoke, chugs a little and then runs fine. Takes me about 3 hours to cut my lawn. The mower has stalled as many as 5 times and as few as zero times. I live on gently rolling hills. Very little flat lawn area. It may be coincidence but it has never stalled on the level sections, just on the up and down slopes. My dealer is now calling the factory service rep for the second time and we still have no idea what could be wrong.