Check the spark plugs before overhauling the engine.
How long have you been shooting a stick? The reason I ask is because if you a new or fairly new to the game it is very possible that when shooting you are not reaching measured draw length or you are creeping the release and, again, not releasing at your measured draw length. Both can affect the stored energy of the limbs and, therefore, increase/decrease the reactive stiffness of arrow spine.
-You state that your bow draw-weight is 30#@28" and your draw length was measured to be 26.5".
-In that that your draw length is less (shorter) than the factory stated 30#@28", I would use a scale of 2#-3# per inch less than the 30# draw-weight of bow.
-That would calculate an estimated draw-weight of your bow to actually be in the ranges of 26# to 27# draw-weight
-If you are creeping the shot, or your established anchor when shooting is less than 26.5", then it is possible you are affecting the stored energy even more.
-Scale the bow at 28" to obtain the actual draw-weight at 28"....regardless what the bow is marked to be.
-Mark a couple of shafts at 26.5 and have someone stand to the side while you shoot several strings to observe whether you are consistently drawing more or less than 26.5".
Once you have reasonably determined the actual draw-weight being obtained, then and only then determine what arrow spine and total arrow weight is best for your bow. Once you have, then tune the bow...and your shooting form. I don't shoot carbon so someone more familiar with carbons will need determine what spine (size) and setup is best for your rig.