Suburban has low power at WOT
 

I am trying to help my Dad get to the bottom of his low power issue. His truck is a '99 Suburban, 350, with 150k miles.

The symptom is that under load at WOT or mostly open throttle, it bogs. He describes that it quits running, no RPM, no power. If the throttle is release and reapplied it can recover. It does not do this every time, but often enough to make him nervous when trying to merge with traffic.

Any ideas on where to start? I replaced the spark plugs for him. He tried a new gas filter (he thinks it may have helped, but time will tell). I encouraged him to tape a fuel pressure gauge to the windshield, but he hasn't done it yet.

Thanks for your help.

Richard