VX KAT
....the adventure BEGINS ANEW! ...2015......
Remember that life is not measured in the breaths you take, but rather in the moments that take your breath away.
Have there been any changes lately in where you've been parking or how much fuel you've had in the tank compared to usual?
Like you, I'd also start to wonder along the lines of temperature changes that would result in pressure changes in the gas tank. Seeing as how this is summer in Phoenix, it might be the opposite of what is sometimes known to occur in winter. A gas tank that's run close to empty in the winter is more likely to get an accumulation of condensation after being warmed up by the exhaust system.
Has there been a lot of pressure released when you've eventually been able to get the caps loose?