Did you remember to replace the black plastic interrupter cup and slide it all the way on the shaft? Also make sure the 4 wire quick disconnect in firmly plugged into the RPM sensor board where the interrupter cup is.

Yes. Interrupter cup is in place and the quick disconnect is plugged in. We even thought the plug might have been plugged in backwards, but this was impossible to do because of the length of the wires.

Did you replace the worm gear too? If so you may have the motor shaft pushed too far forward. Loosen up the couple on the back of the motor shaft. On the front of the motor where the shaft pokes through push it in as far as it will go and hold it there while you tighten the coupler back up and then try it.

WOW, GRISNC, you are having the exact problem I'm having. I have a post also on this same issue. I replaced my worm gear etc. and door will only close 6 inches also. It goes up fine but won't go down more than 6 inches. I have to trick it to get it down, hitting the button to stop it from going up etc. and doing it over and over till the door finally makes it all the way down. Let me know if you solve your issue, I have been stuck on this for almost a month now. Good Luck!!

Doorguy, where is the coupler on the back of the motor shaft that you refer to?? I got up and looked at mine and I think that is my problem, my motor shaft has some play and if I push it from the back it moves forward an inch or so, then I can push it back as well (the play I refer to). I don't see anyway to tighten this up though, is there supposed to be something on the back side of the shaft?? I think I'm getting somewhere now, but just need to know how to tighten this shaft up to remove the play that is in there, this might be why door goes up and will not close. Thanks!!

ALL FIXED!! Thanks Doorguy, it was the motor shaft being to far forward. I had to loosen the nut thingy with the two allen screws in it that goes at end of shaft behind the plastic cap and push the motor shaft back, then tap the nut thingy down further on the shaft and hold it on tightly as I tightened up the allen screws to secure it, causing the slack I had to go away and the door now opens and closes like new!! Thanks a ton for your help on here!!

Sounds promising. Thanks for everyones help. I'll try the same solution and hope for the best. Again, THANK YOU everyone. I know it doesn't get said enough in these forums.

The Coupler just needed to be tightened down on the spring washer at the end of the motor shaft. Took a total of about 3 minutes.
I didn't say this earlier but this door was my Mother-in-laws. You can only imagine the heat I was feeling around the ole homestead while "Mom" couldn't park her car in her garage. At least it only took a week to solve the problem.
Thanks again guys, your help was greatly appreciated. I guess I won't have to sleep on the couch tonight.