Carb Fuel Pressure Fluctuations
Couple of things to check here.
1) Connections at DPU and at the fuel press xducer. You probably have the older Hollingsworth type connector (4 blade connectors). These are susceptible to corrosion/dirt/grime getting on the blade connectors, often a quick scotchbrite cleaning of the blades and solvent clean of the receptacles will solve the problem. NEVER clean the transducer itself with solvent. Also check for snug connections at the DPU.
2) Check the tap line for the fuel pressure to the xducer. Air trapped in the line can cause high indications after shutdown due to thermal expansion. If air is in the line, check all fuel line connections for security.
3) Fuel pressure xducer reaching the end of service life. Often the xducers begin to get "flakey" after long time in service becoming less and less stable in pressure indication.
4) If you don't have a snubber fitting, you may try that. Carb fuel pumps put out a pulsed pressure profile that can cause fluctuations on the FP xducer. A snubber fitting will often smooth those out at the transducer. The snubber fitting screws on to the end of the xducer and into the tap line.
All the engine parameters are "hard burned" into the main program EPROM chip per mfr specifications unless it was a custom software for a special application. So whatever Lycoming's max fuel pressure is for your engine is what's programmed into the VM1000, if the pressure meets or exceeds this max, the VM1000 alarms.