Truck dies under load

[SilveradoDude]

My truck (85 Silverado, 305, 4bbl Q-Jet) will not even hold idle under load. I adjusted the curb idle over the weekend and that helped a little but it was really a stop gap.

I checked the selected items:
1. The choke works fine, in fact the choke works great. No problems. The truck started on the first turn.
2. The distributor is bolted down fine.
3. The truck idles rough in Park and completely dies when put under load

The carb is a rebuild, around 6 years and 20K miles old.
Any help is appreciated.