Generator does not exactly follow the path

[F.A.L.]

i don't use build in controllers to move along the path, I need special moving and data processing and curvy controller doesn't meet my requirements. I took part of the code from the controllers and everything was ok until I made hills. My object now constantly goes into road mesh or fly over it. I do not want to have extra calculations to move like Volume Controller, but I want generator exactly follow the path! Is there a way to solve my problem?