I have a 04 Chevrolet Cavailer an it won't kick in to passing gear when you first pull out unless I run it about 4000 rpms for awhile and then it will jerk reel hard and go and after it finally kicks in it and theen it runs fine until I stop and it will do it again. I have changed transmission and vss( vechile speed sensor) and when this started my speedometer stopped working also? Any suggestions would be appreciated.

 

does the speedometer work now? have you checked your fluid level?

 

ditto
the vss is a very important input to the trans for shift control.