Fuel pressure behavior

Am trouble shooting a hot start issue on my 456GT and had gages hooked up to both fuel rails then other day. While running both side hold at about 50psi, but the right side ( passenger side) had a frequent bounce. When i remove vacuum from either pressure regulators, the PSI goes up to about 60, but the behavior of the gage stays the same. I did swap gage sides too.



Injectors were recently sent for service, filters changed in the last 2 years.

When off, the pressure in both sides raise about 5psi due to expansion, and both sides hold steady while cooling.

Would this be a regulator, pump, or injector issue? Or electrical somewhere towards the relay board
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I wasn't thinking the drop while running was necessary related to my start issue, just wondering if it's a sign of something else to be needing eventual attention. Both Cam and Crank sensors were replaced over the winter, with no change to starting behavior.

As far as my actual issue, Its been frustrating trying to troubleshoot thoroughly and having no results yet. Its a 1995 456GT. When running, from cold or once started hot, it runs fantastic and consistent.

Guido fuseboard upgrade
Coolant sensors replaced under the manifold.
Connections checked, sprayed with cleaner as best as able.
Original Fuel pump, but supports have been replaced and rubber in tank removed.

Has a COP kit, and still Need to still check spark while cranking hot. Starter turns over strong, and battery is newer AGM with normal output numbers.