I have recently bought a hitec 5625 and I am wondering if this will be a good throttle/brake servo for my truggy?

It would not be my first choice.

8th scale needs lot's of torque,
and truggy needs even more.

Will it work: yes
Just not the best servo for the application.

What one would you recomend?

cherck out the HS-7985

It makes plenty of torque for buggy, maybe a little soft for truggy (heavier, more traction, larger diameter wheels, same brakes). If you're on a budget, the 985 model might be a good chioce. It's fast, strong, not digital and lower cost then the top servos.