"Frostburg," and talking about "cold starts." :laughing: Anyway, yeah, you can see some colder temps there (I'm in a very moderate climate, GPs help, but one can get by in a pinch).
If you're looking to replace the GPs (had thought you'd already done that) then the best tool is patience. Start putting penetrating fluid around the bases. One could lightly tap on them from time to time . When going to put a socket to them make sure you're on them square. If you have a torque wrench I'd recommend using it so that you limit the amount of torque you're applying. No idea what the toque specs are for the ones you're dealing with, but I'd limit the extraction force/torque to no more than twice what the installation torque spec is. GPs that have been installed for a long time will end up bonding (threads locking) to the head. For example, my cars' GPs are spec'd at 11 ft-lbs; it's noted to not exceed about 25 ft-lbs for extraction: this is an aluminum head, which for sure one has to be careful with. While it may seem counter productive, often times FIRST TIGHTENING a nut/bolt/GP can help loosen an established bond; however, one has to be very CAREFUL not to exceed a safe torque; go very easy, stopping when there's movement or you hit that torque limit. If you had success in tightening (breaking any bonding) then add a little bit of penetrating fluid and remove! IF things won't budge do NOT FORCE, otherwise you'll break a GP and then be in for a lot of fun (use time/patience up-front lest you end up using a LOT of time and frustration later).