You don't need a ford one just a decent one, seen a few fse give this exact problem, where the rail pressure keeps altering, can even happen to older ford ones.
I changed mine today for a RS500 one on me sapph, as had fluctuating fp, perfect now, cut ring off around old one and took bits out, there was a small spring inside with a pintle on the end that was broken, but main spring and diaphragm was ok.
Have you looked at CTS value ?
tabetha