When I start up my car for the first 10-15minutes my car really shakes through the gears and feels like its really struggling to go
recently replaced fuel filter mechanic reckons possible balance shaft or something?

I recently had the same problem with my tr magna. im not sure if your shaking is the same as what mine use to be like. As a result of a head on collision, the whole front end of my car had to be fixed. When the car was repaired I would drive it and the whole cabbin would shake and have a very low sounding ear pearsing noise. I took the car to my mechanics and he told me a trick as to how to fix this problem. The cure to my shaking problem was by doing the following:

1. Start the motor.
2. Release the motor from the Engine mounts.
3. Let the motor sit and then tighten engine mounts.

Do you get my drift? My motor was tightened in a position that would create noise and wasnt running smoothly. I hope this can be of some help to you and maybe others who have tried everything else. As a cost factor; try asking your mechanic to do this before he starts getting into the expensive stuff.