Gator not charging at lower RPM

[avenirfarm]

Hello all - First time poster. I have an older model JD Gator 6x4, gas with the square headlights. I love this gator... Have been gradually fixing over past couple of years and honestly can not live a day without here on the farm. Recently encountered a problem where it will not charge at low RPMs. Replaced the stator, the coil in the past year. New battery and new voltage regulator most recently but problem remains. Maintenance man has checked all connections and says there is nothing draining. The odd thing is some days I can barely get through the day without having to charge. Other times it can be a week or better. Any ideas? TIA! Donna