Outer Limits 4x4 Board

i have just bought a 2004 gu patrol ti its a 4.8ltr 5spd auto,i purchased it from a car yard & they told me there was a problem with the potentiometer on the sender unit so they replaced it with a brand new genuine unit (apparently) & they are telling me it needs to be recalibrated to the cluster on the dash.has anyone heard of this before coz it all sounds abit far fetched to me i would of thort if you replaced a component with a genuine part it should all be in sinc with one another still?
i have read on alot of forums these patrols have alot of fuel guage issues due to poor earthing from factory so when my mrs isnt at work i am going to put a few earth straps on to see if it will help.i ahvnt run the tank dry yet but from what i have worked out with the k's the guage isnt far off if it is out.the sub tank light was on the dash when i picked the car up but i put a new heavy duty battery in when i bought it so from disconnecting the battery it cleared the light.
iv been told by a few people i can calibrate the fuel guage & cluster via obd( scantool) but our useless peice of shit scan tool at work will only let me read engine control & transmission thats it,there is 2 parts in the scan as well which is meter & instrument which is where i need to get into but just keeps coming up communication error on the scan tool????????
has anyone had this issue before?