I suffer from exactly the same thing , on the range i hit the ball really well 95% of the time , i practice good habits work real hard on my swing , when i get on the course i loose everything i've been working on ,and i swing like a fool sometimes, i forget to put everything i've been working on into practice, i'm sure its a mental thing , with being on the course a totaly different enviroment to the range effecting
how i swing the club.I really think practicing on grass would help alot.