2000 Silverado Power Door Lock

2000 Silverado, 4 door, V-8, 75K miles.
Drivers door power door lock will not unlock when temperature drops below 27 degrees. Once temperature rises, it works fine. This has been occuring for over 2 years. This summer I lubricated the mechanism with Tri-Flow lubricant, and the lock worked fine. Until yesterday (temp in low 20's). Today the temp is in the 40's and it works fine.