Glad you did the correct test and glad you are going to be SURE of the new one. Real sure, before installing in truck. You have saved a lot of time and headache. The sender was intermittent it seems, but don't conclude that yet. This gas gauge/sender can be a tricky business. Good job. Don't throw the old sender away yet. Let us know the final outcome.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn