Both the genuine GM part and the BOXI strut shown in post #13 are the correct length.
The GM part # is 19330118. About $25 ea. It has the original style clips which are dificult to snap on, especially the lower one in very limited space. If you use this strut, tie a string on the clip you use at the lower end. Otherwise if you miss and drop it, it's lost. Also keep the original struts so you have extra clips.
The BOXI uses an odd shaped hairpin clip that's very easy to use. You slide it into a tiny set of holes and then rotate it and it snaps over the shaft. However, you can't get your hands into the space at the lower end. Get a pair of 8-10" forceps. The only easy way. Again, careful not to drop it, the cavity below the lower attachment point is totally inaccessible. You drop something there, it's gone. Also, the BOXI struts have screw-on ends. Make sure they are screwed all the way in, otherwise they will be too long.
Many thanks to Convertme for post #2. Without that hint it would never occur to me that the struts could be the wrong length.