Well, my car is put away for the winter, but on my last ride I developed a problem and I think it related to a bad fuel pump (Walbro). Here are the symptoms:
Whenever the manifold vacuum gets close to 0, the car will not develop any power. I'm lucky to make 20 mph. It stumbles and misses and the AF ratio is all over the place on the lean side. Yet, with the car in neutral, it idles fine and revs throughout the rpm band fine. My first thought was that the GM 3 bar map was bad, so I swapped it out. But no, that wasn't it. So now I'm thinking fuel pump. What do you think? Should I order a new one?

 

In my experience, the best way to spot a fuel pump going out is to watch the A/F on a dyno pull. They generally run out of fuel up top and go lean.

 

I just replaced my fuel pump because it was going bad. My symptoms were as follows:

Fuel pressure would slowly drop while driving car (would take an hour or 2 to get critical).
While idling, the pump would make a very loud whinning noise
When trying to accelerate (before boost) my A/F shot up to ~17-18
EGTs got much hotter (I was seeing 1400F+ when I hardly ever see 1300)
My idle fuel pressure with vacuum was only ~230kpa compared to a normal 320kpa