The problem I'm having involves erratic speed which only happens when the tractor has been run for over a half hour or so. It never happens when cold or when at full throtle. What takes place is when you back off the throtle to say 1/2, power to the axle drops to zero for a couple of seconds and then sharply engages. I have replaced the shock absorber (throtle dampener) which has not helped. (The Deere manual indicates this part could cause erratic speed problems). The mower has been doing this for a couple of years now (mower used for my residence only, maybe 50 hours per year.) The problem started all at once and has not gotten any worse. Any ideas would be appreciated.