I have a hustler super Z with the 28hp Kohler EFI engine. It runs fine if you use it here and there but on days we bag with it and run it for long periods of time at low RPMs it surges rpms up and down and almost dies tell it finally does and the battery is dead. The battery was replaced in May and I believe is fine. I'm thinking that the voltage regulator is getting hot and not working properly over long periods of time. Any advice?