Transmission makes vehicle slower

I’m currently working on a semi-realistic racing game and I’ve gotten up to implementing a transmission. However, whenever I shift up the car just starts going slower.
Does anyone know a solution to this? Any help would be appreciated.

Like what? Is that about acceleration? Or simply car current speed?
And if you want to make realistic vehicle physics, You may find this site helpful.

The car loses speed whenever I increase the current gear of my car which is most likely caused by the lowering of the applied torque. This was the reason I made a forum post a yesterday trying to see if it was possible to make a custom wheel collider that would attempt to reach a target rpm using a certain amount of torque.

Hmmmm, I’m making vehicle physics with custom wheel collider, but gear system does working. Always apply torque is about few thousand. If you want to resolution fast, i think you need to post with videos.

If you stop accelerating in neutral, does the car keep going or does it come to a halt relatively quickly? In other words: are there any external forces such as drag slowing your vehicle down? That’s the only possible explanation I can come up with for a lower torque causing the car to slow down.