If I read this right, you have some transmission trouble but you can deal with that. OK
If you need to improve road handling you need to let us know what problems you are having.
As for your lack of sound, I figure it's an aftermarket unit and it could be any number of things. I'd start by making sure my speakers haven't been destroyed by rain, puddles, floods or anything else, then make sure the wires are still connected to them. If those seem OK then you need to make sure the wires to the player are still connected to it. This part could be easy or a slight nightmare depending on what the installer did, or didn't do.