2003 Yukon XL 5.3 Chugging

[dumb dummy]

We're working on the above vehicle, customer drives it approximately 4 miles to work and 4 miles home. She says the car is "chugging", no dtc's are stored in the computer. My initial thought is vacuum leak but every car we work on seems to have fuel problems so that's at the front of my mind. Last week she brought it by but it wasn't running bad, we replaced the fuel filter(it was somewhat clogged), checked the fuel pump pressure(all good), and sprayed a can of mass air low cleaner through the intake. Anybody ran into this?
Thanks

[maxwedge]

Did you get the condition?

[dumb dummy]

What condition would that be?

[maxwedge]

The condition meaning what the customer is saying is wrong, did you see it happen? Any sign of misfire history, how is the long term fuel trim.

[dumb dummy]

She said it's chugging, perhaps I should buy it a beer. Yesterday we cleaned the throttle body, it hasn't acted up for us other than the last time when we were backing it over the lift and the engine sounded like it stumbled when it got put under a load. NEW INFORMATION: She said it only happens when she's backing up. Hope this helps.
Thanks,
DD

[maxwedge]

Hmm reverse only, look for some opening or crack in the air intake behind the maf, if it is set up that way, as the engine torques in reverse, this could happen.