I'll take a guess and say the fuel level is too low in the secondary float bowl.
When you say its popping,
It's popping out the carburator right? And not out the exhaust?
Is it vaccum secondaries or a double pumper?
Did you set the float bowl level first when you put it on your truck!? - With it running, Remove the sight plug on the side of the float bowls then use a screwdriver and 5/8" wrench to adjust the fuel level till it barely runs out of the sight plug hole. Might want to get a rag or cup to catch the gas if the level is set too high.
Make sure the vaccum diaphram for the secondaires is working and not blown. You can move the linkage to WOT then with your other hand push up on the vaccum secondaires rod on the left side of the carb. You'll hear it go PSSSHHHH.
If you did that, Take it off, take the float bowls off, blow everything out with carb cleaner and compressed air.
Then when you have it apart you can check the jet sizes. You said it popping when you get on it hard so check the secondary jets and you can compare them to whatever is stock @:
www.mortec.com
Also check the power valve on the primaries and make sure the diaphram isnt blown.
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