Mass Air Flow Sensor or Cat problem???

1997 Chevy 1500 Series Pickup with a 4.3 liter vortec V6. Truck is running fine but has poor throttle response at midpoint of acceleration. Changed the throttle position control sensor even though no codes were coming up on handheld computer to indicate this was the problem. It did not fix the problem so that was not it. We then took the truck to the Chevy garage. They put it on their computer and found no codes indicating any problems as well. They suggested that it might be the mass air flow sensor and suggested disconnecting the EGR valve to see if that made a difference. With the EGR Valve disconnected, it drives perfectly. However, they tested the EGR Valve and found it to be working perfectly. Again, they stated that they THINK it is the mass air flow sensor that is causing the problem, and said that if that didn’t fix it, they had no idea. They did not have one in stock and said it was $400 for the part. We found the part at an auto parts store for much less, but hate to spend a lot of money on an electronic part that cannot be returned if that is not it.

Today we checked the readings on the mass air flow sensor with the handheld computer and came up with the following: At 700 rpm’s the Air intake temperature was 57 degrees and the engine temperature was 177 degrees. The reading for the mass air flow sensor was 0.59 lb/min. At half throttle (about 55 mph), the reading was 3 lb/min and at full throttle (about 75 mph), it was 8 lb/min. We can’t find anything to indicate what the readings should be so I’m looking for advice on whether you all think it is actually the mass air flow sensor that needs changed or if you have some idea what else it might be.

The only other thing we can come up with is possibly a problem in the catalytic converter. Any thoughts or ideas on this would sure be appreciated!

Thanks!