TBI high rpm problem

[smashingchuck]

Background:
1991 TBI 350, 700r4. 125,00 miles on the engine. The plugs have about 5000 miles on them, the cap and rotor about 10,000 miles, and the plug wires about 40,000.

I have a problem with my truck that is progressively getting worse. It idles fine, and accelerates fine, but anything past about 1/2 to 3/4 throttle that damn thing just spits, sputters, and goes NOWHERE. It used to only do it at WOT, but has also progressively worked its way down to 1/2 throttle. Today when I started it (very cold) it almost did it right off idle. It does seem to be worse when the weather is cold out. I ran a bottle of Lucas fuel condition through it the other day, it didn't change a thing. I tried higher octane fuel as well, and that had little effect on it. I'm thinking this is somehow fuel delivery related, but also think it could be ignition. I really hate to just start throwing parts at it... anyone have any ideas?

thanks
chuck