1999 Lincoln navigator sputtering and slight lose in power

always good to clean the throttle plate with carb cleaner spray after removing rubber duct intake hoses, The temp rise may be low coolant or air in system going around, or a slipping water pump at higher speeds from a loose belt

Would cracked/bad gaskets cause this? I was told there is coolant flowing into the packs/plugs due to gaskets needing to be replaced.

Yes you can clean your throttle body but that's not your problem your problem is to change your coil packs and plugs all of them

And for the sputter change air filter check your gas filter or do a gas pressure test check out the spark plug as well make sure they're not corroded especially spark plug number 1 and 6 spark plug