Just sounds like the weather then I'm afraid. I had the same issues with my WOC. Britain is only good for GBBRs for about 8 months of the year.
A couple of things you could check are just the basics: Firstly, make sure your gun is well lubed - any additional friction is going to cause issues. Second, check your hammer spring is sufficient to get a full depression of the outlet valve. Although is shouldn't be the issue with WE pistols, the TM ones require upgraded hammer springs to hit the valve hard enough to dispel gas. This would explain why it's the same at room temperature (which it shouldn't be).