I have often wondered why they seem to be affected by temperatures, I knew they used Nitrogen for its stability in temperature variances (i.e. the physical expansion characteristics of the gas at a given temperature range.) So I can only assume the reduction in extension speed/strength is a result of the shock fluid's viscosity (which I would have thought would have been equally chosen for wide temperature variations?)
I notice on many vehicles and implements with gas charged shocks, be it hoods, trunks, hatches, hutches, the top of my tool cart, ect. all seem to react slower in colder weather (i.e. sometimes I can just let the hatch sit at half height or my tool cart lid doesn't open when I unlock it; but if I just gently assist it a little it slowly pops open), yet in hot weather they almost fling open (during the summer months I can't leave my tool cart unlocked because the lid always wants to pop open and my hatch will go from about 1/4 open to fully open by itself in hot weather.)
Post Note-
Be thankful you don't own a Lincoln or Ford SUV with the automatic tailgates, those things barely open all the way and I've smacked my head on them a couple times doing used vehicle inspections (and I'm barely 6'-ish). It seems a lot of those automatic tailgates sacrifice a bit of arc (in terms of fully opened position) for the feature, in the case of the Lincoln/Fords I have no idea how you're supposed to load anything in them, I almost always had to duck under the door somewhat to get in there.