I am replacing a leaky head gasket and noticed that it looks like a lot of carbon buildup considering that I drive probably 70% freeway miles on the car. 147k miles.

What do you guys think?

This year I replaced the idle air hoses and all rubber vacuum components.
Last year I replaced plugs/cap/rotor on the ignition-side and the o2 sensor.
2 years ago I had the fuel distributor and eha rebuilt and matched and injectors replaced. fuel filter replaced last week (it was a little overdue). Fuel pumps are original. Duty cycle fluctuates around ~48%

I am getting about 20mpg average fuel economy.

Some photos from today:

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k