I had my old and cracking garage door replaced yesterday. It took about 4 hours and the guy was courteous and seemed to know what he was doing. Overall, he did a good install, but It looked like the door wasn't level when he finished. I asked him about it and he said that my floor appears to have settled and the door frame is not square. There was about and 1 inch gap between the floor and weather seal on the bottom of the door on one side.
Next morning, with my level, I checked the floor and door frame and found it to be level and completely square, but the door was still misaligned. With my tape measure, I began looking for what was uneven. I found the door track misaligned, and I corrected it, but the door was still high on the east side.
I continued to look and discovered that the wire (counterweight) on the west side was loose when the door was all the way up and the wire cable on the east was very tight. Both wire spools are connected to the same shaft, but their tension was VERY uneven. Having some experience with tools, I easily corrected the difference in tension.
With the tension now being even on both sides, the door completely closes and appears even and level with the floor and door frame.
Additionally: I discovered several of the self starting metal fasteners to have been overly tightened and partially stripped out. At some point they'll need to be replaced with a bolt and nut, because the stripped screws will loosen over time.