Sudden drop in rpm while driving

[live2pull]

04 Denali. Losing approx. 300-500 rpm randomly while driving, or idling at stop light. Only happens when in D never in P. Tested fuel pressure and while Key on engine off, fuel pressure jumps to 60 then bleeds down to around 40. Key on engine on rock solid at 60psi. No CEL. Could the fuel pump be the issue. Unsure how to test the relay, or if the relay just typically fails 100% without warning. I don't think I have a serviceable regulator. Throttle body is new. Just kind of stumped on this one on what to check.

 

[PNWYukon]

Any codes?

 

[OR VietVet]

I would want to see what the fuel pressure is while driving and not just sitting still. If do a pump I always recommend doing the relay at the same time but doubt that is your problem. I would also want to get a back pressure test on the catalytic converters. How old is the fuel filter? When was the last time you cleaned the throttle bore?