Make sure the gas cap is vented. Drive it with the cap loose & see if that makes a difference. Check the sock on the bottom of the fuel pickup tube in the tank if it has one. Look over the fuel lines from the tank to the carb for any filters that may have been installed. See if they are clogged up.
You didn't say what year truck it is & what model carb.
Jon G it sounds like your float drop is not adjusted correctly.
George
