[BigMikeISF]

Is the car in sport mode when this happens?

 

[BigMikeISF]

I've had this happen to me but I was in sport mode and driving it pretty hard. It wouldn't shift gears and I was cruising above 4k RPM's down the freeway for quite a bit of time until it finally shifted up. I didn't think anything of it other then it just wanted to keep me in the right gear so it didn't have to downshift when I pressed on the gas even harder. I agree with Fig in that I don't think it's anything to worry about.

 

[BigMikeISF]

mine had the problem for the 3rd time today. it has 1004 miles on it. it happened when engine was cold after i had driven for about two blocks. i was in normal mode and outside temperature was 55 degrees.
i am not convinced it is a build in feature of the car. if that's the case, it should happen much more often. i am not suprised your dealer has no clue since they probably sold very few F so far and this problem doesnt seems to be universal. i hope in a few months, Lexus will have better clue as more people complain about it.

I would report yours to the dealership as well. If a bunch of individuals are reporting it, Lexus will look into it and make sure everything is alright with the transmission. I don't think it's anything to be worried about but you can never be too sure

I have had the unfortunate pleasure of having to drive the IS-F this winter in the NorthEast because the "beater" car is well, not working (ironic).
Seems to me, the IS-F just hates the cold. In the low teens or single digit temps the engine noticeably studders on start, the shifts are not nearly as fluid, and the in-dash display gets stuck if I try to change to another screen. These problems go away after a minute or two of idle or driving.

I've had this happen in previous cars. Once the car gets warmed up and things get flowing, the car returns to normal. I wouldn't be too worried about it