2016 2.7 struggling going uphill

Sounds like you had it floored and the trans chose2nd gear.
I did a calculation for you. 70mph in 3rd gear (1.49 gear ratio) with stock tire size is about 5000rpms. Sounds normal to me. You can try manually shifting up and it might hold a higher gear but it sounds to me like you are flooring and the trans drops to 3rd for that speed. If it is taking a while to shift up again after cresting a hill, try letting off the throttle and see if the trans responds quicker.

 

Partly wife got pissed when I threatened a manual and partly cause I couldn't find on that checked the few required boxes I had when I was shopping.

 

MBE350 with 3.5L V6 compared to this 2.7 I4 - yeah, the 2.7 doesn't have the power and perhaps the torque as the E350, plus it may weigh a little bit more.