Ok, so my gas mileage/EV problems have been well documented on this board. But I've started noticing a pattern that has me stumped.

If I just get in and just start driving, it'll take a good 30 to 45 minutes of solid driving before the ICE will shut down and kick into EV mode. Then, even when it does (at a stoplight or wherever), I usually can only get to about 5 mph before the ICE kicks in again.

BUT...

If I get in, drive two blocks to the bank. Turn the FEH off. Go get cash from the ATM (total time: 1 minute). Then start driving again? It'll kick into EV mode almost immediately and I'll be able to get up to 20 or so mph before the ICE turns itself back on again.

And the even weirder thing is, it'll stay that way unless I don't drive it for an extended number of hours. If, for example, I park for an hour, go shopping, then start the FEH again? It'll work fine as long as I had that bank stop earlier in the day.

Any ideas what to do? I've explained this to the dealer about 5 times and they keep claiming nothing's wrong.