I have had this problem with corvettes for a while. The new sending units arent calibrated to work with the old gauges. If you sell a part don't you think that you would make it right
. They sell a kit for you to splice in a do-hickey (that's technical for piece of crap) that makes it work. I will never do this. What I do and you will also is to find an original sender and use it. Hope this helps, Rich.