My guess is the new NAPA sender works differently from the old one (different resistance scale). Does the new sender look about the same as the old one (most are shaped like a small can, about the diameter of a quarter or a bit larger, and about 1 - 1.5 inches tall)?

Since you have an Ohm meter, and can't get a reading at all on the new sender, it might be bad. I'd take it back and have NAPA check it against the specs for a new one.