The location of the shock ends, or overall length of the shocks is generated by the game based on the Y location of the wheels, 6 inches above absolute center for the bottom, and for the top ends of the shocks, that's determined by where the centerline (Y=height) of the truck body.
You cannot directly edit the shock model itself, except by raising and lowering the wheels or truck body model.
The easiest fix for the truck you're working on would be to open the axle model your truck uses with binedit and resize it's Y and Z dimentions (height and length) a little bit then save it with a NEW name and edit the Axle Model Name line of your trk file accordingly.
If you use binedit's truck editor it will display the shock end locations exactly the same as the game renders them so you'll know what your going to get before you try out the pod.