Stroker Motor wont Rev pass 5200Rpm

Is your ignition boost reference, ie does it retard under boost? You could be running up against this. If you have a retard controller (MSD) you can retard ignition 1 degree per PSI and see if there is any effect. you could also dial back your timing a tad and see if affects top end only, it will disturb bottom end but will give you an idea on what the motor likes up top under boost. Stroker on boost and running that high in RPMs is a combo that will require some careful management as those 3 usually don't work together easily. Whats your compression?