Gas gauge problem/question

[SnowNeck]

The other day I replaced my rear mounted gas tank in my 85' went from a 25-31 or so, the depth of the tanks were about the same so I used the same sending unit. After it was all finished I started the truck up to notice the needle on the gas gauge was bout a nick past full at bout 180 degrees. Doesn't seem that it's moving at all either. Put some more gas in it and drove it, no movement, now is this a sending unit issue? Ground ? Or should I get a new gauge being that I went up in size.