My car is a 2020 Ford Kuga, the corresponding model in the US is the Escape.
I am currently running the latest version of comma/OpenPilot, but this issue was also present in the 0.9.x versions.

The Core Issue: Slow Acceleration and Inconsistent Speed Setting

When I engage self-driving (OpenPilot) and set the speed limit higher, the car fails to accelerate up to the set limit. For example, if my current speed is $40\text{ km/h}$, and I engage OpenPilot and raise the maximum set speed to $80\text{ km/h}$ with a clear road ahead, the car only gradually increases speed to about $45\text{ km/h}$ and then hovers between $45\text{ and }50\text{ km/h}$. If I manually step on the accelerator to bring the speed up to $60\text{ km/h}$, it will then only maintain a speed between $60\text{ and }65\text{ km/h}$.

Comparison with SunnyPilot (Previous Fork)

I previously used the SunnyPilot fork, which did not have this specific slow acceleration problem.
However, SunnyPilot had a different, more aggressive acceleration issue:Aggressive Shifting/High RPM: Even when set to "Comfort" or "Standard" driving modes, when the system needed to increase speed, the engine RPM would often rise to around $4000\text{ RPM}$ before shifting. Sometimes it would even hold at $4000\text{ RPM}$ for a second before changing gears.

Contrast with Stock: The car's built-in Level 2 system typically shifts at around $3000\text{ RPM}$.

Starting Gear (First Gear) Hazard: The most problematic part was when starting from a stop in 1st gear. The system would frequently rev up excessively. If I didn't immediately step on the brake to disengage comma/OpenPilot, the RPM would rev up to $6000\text{ RPM}$ and sustain it for $1\text{ to }2\text{ seconds}$ before finally shifting. I am unsure how to resolve this high-RPM issue.