[D13]

Let me see if I understand.
You pushed the pedal to the floor and held it there.
The engine accelerated for 10-20 seconds, then stopped accelerating but did not stop running.
You let off the pedal and then you could get the engine to accelerate normally.

If that is so, 3 things come to mind.
First and most likely, you probably ran out of fuel. The 292 is a big motor for the single barrel carb, which does not hold a lot of fuel, and has a fairly restrictive fue linlet. You probably got the fuel bowl drained. When you let off, the fuel needs dropped and the bowl refilled. You can get a bit more by raising the float slightly, and/or raising the fuel pressure via an electric pump and regulator (which will be overkill for the carb), but this will help only a little. The real cure for this is more carb with bigger fuel capacity and bigger inlet.
Second, you ran out of breathing. The 292 moves a lot of air, think of it as a 400 SBC with two holes missing. The head is not particularly good flowing, and the carb is restrictive. So when trying to move a box shaped truck thru the air, the engine is trying to breath a lot of air, and the carb and heads will, at some point, limit its performance.
Third, if it's an automatic, you may have gotten to the breathing limit in the engine without the trans shifting to the next gear, which would drop the RPM and let it work.

I highly recommend you get a copy of Leo Santucci's book on the inline six (the second edition just came out). It's more race oriented but there are some good sections about carburation. Also inliners has some good info on their site.