po300b 2002 denali

[Robert G]

hi ; i am having issues with my 02 denali. i have a po300b code. i changed plugs . when doing that i found all plugs to be clean and gray/tan. ( may be lean) i then cleaned the injectors. after a test ride the code came back. tested fuel pressure and found 45 psi at idle, 55psi with vacume removed. with vac. removed the misfires on cyl 2 and 6 lessened a great deal. dose anyone have any recomendations on further diagnosing the f.p.r. and pump. any further tests to solve this issue would be appreciated . tks