New aftermarket unit

So, I did a search of topics about fuel sending unit problems.
None seemed to be quite like mine.

So I got this new aftermarket fuel sending unit from Autozone.
It's Spectra Premium brand part #FG89A.
Hooked it up and had no problems for the first day.
Since then though, It never reads the fuel level right.
It's NOT that it reads as full or empty all the time.
Some days it'll read empty then you'll take another drive an hour later and it reads the correct amount.
Today I put 20$ of gas in and it reads at a quarter tank. That is NOT correct.

Is the sender just bad?

 

Sounds like the float or arm is rubbing on the side of the tank, or getting hung up on something inside.
But first make sure the connections are good, especially the ground wire.

 

I just don't see how it would be hung up.

 

Wait a minute.....Are you not suppose to use the plastic float piece that it comes with, but your old brass one? Some goddamn directions/instructions in the box might help, because I asked two people and they didn't seem to know either?

The tank is 20 gallon for V8 and that's suppose to be(according to the manufacturer's website) the right sending unit. The gauge pretty much reads empty most the time now.