m15 R2, OLED slow FPS

Hi Everyonem

This is a weird one! 

I purchased an Alienware M15 R2 OLED (i7, 270 MQ, 16GB RAM) two weeks ago and love it.

However there is one peculiar bug, as follows.

Playing Forza 3 and 4 as examples (fps displays in game):

When I play on the laptop screen in 4k, I get 40fps BUT when I play with the exact same setting outputting to my Panasonic 4K TV (HDR), with no changes at all: 60 fps! 

I have tested this in every possible outcome I can think of. As soon as I plug the HDMI cable into my laptop the game jumps to a solid 60fps on the TV. When I disconnect the HDMI lead, even mid game, the laptop OLED screen falls back to 40 - 43 fps.

I have heard before that laptop screens can be a bottleneck and using an external display can improve performace but this makes the OLED in the laptop near useless. 

Does anyone have any ideas?

All drivers are up to date via the Alienware Update software and the display is set to 60hz on both the OLED monitor and TV.

The Nvidia control pannel is the same for both the laptop and tv, I do not adjust it. It has got to be a bottleneck with the laptop outputting internally to the OLED.

Thank you very much.

Paul