I recently installed a fuel pressure gauge and when I pumped up the pressure with the lift pump I noticed a hissing from the front of the injection pump area after pressure built up.

Is this a leak that I need to trace or maybe overflow valve engaging or ??????

Truck starts and runs fine. No drops or spikes in fuel pressure. Sits for a few days and still holds prime.

I question this because I lag a little more than I think I should getting to boost. Is this right or needs to be fixed?

Thanks in advance!
Kid