98 Regal fuel pump

Overheating caused my 98 regal to have a new engine put in this week. All good except service engine light says lean fuel on # 1 bank. One mechanic says the fuel pump pressure is 5 lbs too low and that will cause a lean condition at idle. I have no problems going down the highway and I dont notice any rough idle. Any ideas if low pressure can cause the problem or can it be just needing an injector cleaning?