[Mgb-v8] funky fuel gauge

[not me]

i'm having problems with my fuel gauge.  maybe someone can shed some light on
this.......

i replaced the fuel tank and sending unit about a year ago.  the fuel gauge
has be acting weird since then and seems to have a mind of its own.
i have change out to another guage which behave exactly like the other one.
does this sound like a faulty (albeit new) sending unit or could there be
another problem lurking somewhere in the bowels of my car?

comments plese.