Additional info: So today, Oct 11th, got ready to head on out and slides wouldn't work. Kinda expected that so set up an electric space heater with fan on a step stool around a foot from the hydraulic slide assembly. I'd been waiting since 9ish and tested several times just trying to pull in the slides before I went with the heater. Only ran it around 5 minutes and the slides started working. Air temp was 44F. Ok, after a night of 20F, close enough to the temp that previously made it work so could be a coincidence.
this seems a generalization
exactly what did you warm up
the pump
hydraulic cylinders/rams
hydraulic gearing/drivers
solenoids