Sounds like you may have a drive gear going bad. You can remove the cover from the motor unit and check. It may be a good time to get the pro out though as you have additional problems with the door closing.

The gears look great, with no sign of wear or damage. I lubed up the tracks and wheels, and tried it out. Works flawlessly now, but it's warmer today than when the door started acting up. Next cold spell will be the test.

One of my garage door problems is solved - the door completely opens regardless of the outside temperatures.

But, I continue to have the problem with the door not completely closing if the outside temperatures are cold (30F or less); it nearly closes (to within a foot), then reverses to open. Any ideas on what may be causing this?

I continue to have problems with my Python II on cold days, and am thinking about replacing it. I think a 1/2HP opener is just too small for this 20' X 8' door, and when it get cold, everything (springs, rollers, etc.) tightens up a bit.

I am thinking about buying the SOMMER synoris 800 (1 HP). Anyone have an opinion about this opener? I found a few post on other forums about problems interfacing with HomeLink.