Hello. I have a 1/2 hp Craftsman Door opener and I had to replace the gears in it. After putting everything back together and doing a test run the garage door would only open about 4 feet and stop, reverse and close about 2 feet and stop. Now when I run the cycle it only opens and closes about 2 feet which leaves the door open about 2 foot if any of that makes sense. I closed the door manually and tried to cycle it unattached from the door and I get the same thing. Does anyone know what would be causing this. Ive read through some other posts on here and It sounds like it could be my RPM Sensor or circuit board. The only problem with that is when I checked the parts list on Sears.com it said the the part has been discontinued for my model. So basically, Is getting a new opener my only option?