Gear Tuning Parts: Where to Buy?

I've noticed that the transmission in my vehicle (Suzuki Grand Vitara XL7 2.0TD, manufactured in 2004) seems to be inadequately matched to the engine. The first gear is too fast, and the fifth gear is too slow.
Consequently, the acceleration is weak and the top speed is too low.
So, maybe someone knows a way to obtain the necessary parts.

Maybe you could include some information about your vehicle in your signature! That way, people might have a better idea of what you're talking about and what you're looking for. If I remember correctly from another thread, you have a Vitara with a common rail engine? You probably won't find much information here about that. However, there's a lot of information available about VW/Audi vehicles. There should also be a Vitara forum; maybe try posting there.

Yes, there is a forum for Zuki Zuki, but you won't find as many like-minded diesel enthusiasts there as you do here.

Just for your information, I used to drive a Passat 1.9 TDI with 186 horsepower until recently.
But not anymore.

I am counting on your participation, thank you.

There's hardly any experience available here. And who's going to help? Maybe someone in the Vitara forum! Perhaps someone has the ET-NR (engine control unit number).