Two easy test,
One, go to your local station and your favorite pump and add some fuel, hit the road and see if it act ups.
Two, return to the station, same pump, same direction you were facing the first time, add the same amount of fuel. This time, pull forward quickly, slam on the brakes, back up quickly, slam on the brakes, then go for the same drive.
By quickly stopping, you are mixing the fuel and also moving what ever might be in the bottom of the tank.
My guess is a baffle plate has come loose or you have trash in the tank. The added fuel is moving something as it enters the tank. Your comment about only running half a tank or it sloshes out is a sign something is wrong inside. These truck didn't do that new.
