Starting and idling problems

Ok so I have installed an electronic fuel pressure gauge. When you turn the key it primes the pump and reads 50psi, when the engine is running it's reading 58psi. Is this normal for the corvette filter/reg to prime only to 50psi initially?

What is an acceptable drop off in PSI if you were to prime the pump only and then watch the gauge over a few minutes?

Car is still starting a bit rough but then after a bit of spluttering etc for 10-15 seconds it sorts itself out and idles fine.