[VetteVet]

I can think of at least 6 things that will cause your problem and neither of them is fuel related. Here's why. Your truck runs 30 or 40 MPH in between the lights but dies while at idle at the light. Fuel delivery is much greater at 40 than at idle so you are getting plenty of fuel. So here's my thoughts.
1.Vacuum leak
2.poor spark at idle
3.one or more cylinders is not firing, maybe just at idle.
4 Worn points causing retarded timing and slow rpm at idle.
5. carb float has tiny debris in the float needle causing engine flooding at idle.
6.float level too high causing flooding.

These are just a few off the top of my head. There are a few more that are more radical like worn cam lobes and timing chain. Leaky valves etc.

It would be nice if you would post a few details about the engine, trans, carburetor.etc.