I am currently (and have been for 2 years) experiencing the same problem (keep putting it off), especially with the driver side window.
I have cleaned and re-lubed the regulator/flex drive assembly, sprayed the weatherstrip to no avail, in the cold, winter months the window goes up...Sloooooooooooooooooooooooooooooooooow.
As soon as the weather warms I plan on cleaning/re-lubing and replacing the window motor and flex drive.
When lubing the guide weatherstrip/channels do not use an oil based lubricant, use a Silicone Lubricant and allow to dry.
Be sure to clean any dirt/debris from the guides before spraying lube.
Do not use oil based lubricants on the regulator/flex drive/gear assemblies, use a synthetic lube that is water resistant and not affected by temperature.
Also be sure the window motor is actually seeing the proper voltage and that you have good continuity to ground on the ground circuit.