Just replaced the worm/drive gears on my Craftsman garage door opener. Now it will only travel 6 inches up or down!

After installing the new worm & drive gears (41C4220A) in my Craftsman garage door opener, model: 139.53962SRT1, without attaching the chain yet, I re-plugged in the unit. The motor fired up for as few seconds then what sounded like it going into reverse for a few seconds (maybe4-6 seconds total) it stopped. Figuring everything need to be re-installed I didn't worry so much. But after everything was installed the door would still only open maybe 6 inches then close. I read the manual and attempted to adjust up & down knobs but no matter how much I turned the knobs the door would only travel at most 6-inches then close. I double-checked to see if there was any electrical contacts that I left unplugged, but I only disconnected the red & blue connections on the capacitor and the white connector on the ceiling of the unit, and they were connected. Do you have any suggestions on what I can do at this point, saving buying a new unit as my last resort? Thank You!