It's an ok car, but you made a pretty massive mistake.
suspensions.ini sets spring rate to a reasonable 28N/mm, but setup.ini specifies minimum spring rate to 125N/mm at front, and 88N/mm at rear.
setup.ini minimum overrides the 28N/mm in this case, so your spring rates end up 4.5x too high on the front and 3.1x too high on the rear.
This gives you about 6hz ride frequency by default, while after lowering setup.ini minimum it's about 3hz.
The frequent pitting has sadly become a bit of a bug of the car. Without the fuel burn you should be able to do 20 minute races without any trouble.
Feel free to DM me with the issues you encountered :)