1989 C7000 box truck has me pulling my hair out. Auto-Allison transmission and only 32,000 miles but has sat for a year or two at times. new distributor, plugs, wires. Has a Q-jet that seems to flow well and nice conical spray pattern. Starts, runs, idles perfect-but is absolutely gutless. Cannot get truck over 50 MPH floored and unloaded. Replaced both inline to tank and Qjet fuel filters and exhaust seems to be flowing fine-it has two stock NELSON mufflers but no CATS that I can see unless they are integrated into the mufflers themselves.

This truck has dual smog pumps as well (I though smog AIR type pumps were only for CATS and air volume)....still wondering if they are hidden CATS that are clogged.

The engine revs up slow to the governed limit of about 3500-4000 RPM but has no power at all.

Before I yank all the smog equipment off-I am welcome to suggestions-just cannot figure this one out....

Have you done a compression test, I know you said it only has 32,000 miles but it still comes to mind....

I though smog AIR type pumps were only for CATS and air volume

Nope. Before cats, smog pumps where used for NOx reduction by pumping the air into the manifolds. My '73 Nova originally had a smog pump on it, but as you know, cats didn't appear until 1975.
As for your truck, any pinched pipes? Unhook the exhaust from the manifolds and take it for a drive, that'll quickly rule out a plugged/restricted exhaust.

Alex.

possibly timing is retarded? try timing without light;
advance distributor until engine starts to stumble, then
just back it down a little. if the marks are off, or you
have a wrong balancer, your spark could be retarded.