I have a weird issue with my 2016 4Runner Limited:

When going up a very slight incline at low speed I get a sputter / stutter in the engine or drive train (I cannot tell which). It occurs only when the engine is around 1100-1200 RPM and speed is anywhere between 15-30 MPH. It disappears as soon as I step on the gas a little more. It does not happen every time that I am on a slight incline but enough to where I am annoyed by it.

I just replaced the ignition coils and that did not do the trick like my mechanic and I thought. The spark plugs are maybe 2-3 years old. When I hook up my little handheld Motopower scanner it does not pick up any codes either.

Any thoughts on what the issue might be?

When was the last time you changed the fuel filter? If it’s been a while, it might be clogged and causing fuel starvation.
Also, check the throttle position and mass airflow sensor for any issues.
Inspect the transmission fluid level and condition.
Plus, check your air filter. A clogged air filter can restrict airflow to the engine, causing hesitation or sputtering.