Fluctuating fuel gauge

If the new fuel pump assembly came with a new sending unit on it, I would try to re-use the original sending unit, otherwise the issue is with that new sending unit if this issue was not there before it was replaced.

Here are the instructions on how to change out the fuel level sender. Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.

And a bit more on the sending unit. 'if' it wasn't installed in the proper position on reassembly, that could also cause an issue because of sloshing fuel constantly moving the float and thus sending strange signals to the gauge. I've done that on my own vehicle. And it drove me nuts till I dropped the tank again and put it in the proper position. Also, could be bad resistance wire on new sending unit. When it crosses bad spot, sends strange signals too. Hope this helped. Dave