Installed '90 GM Factory EFI tank, '72 Blazer Factory gas gauge is pegged past full?

[Okie528]

Installed '90 GM Factory EFI tank, '72 Blazer Factory gas gauge is pegged past full? I know the ohms are the same, just curious if anyone else has run into this problem, and how I can fix it. All my wiring harnesses were replaced before the tank swap and gauge was working properly before. Wire is grounded well. Tested the sending unit with a multimeter it works properly. Assuming I need to do something to get the newer style sending unit to work with the factory fuel gauge. I did the swap so I could use an in-tank pump for my Holley Sniper EFI. I have posted this in the Blazer Forum and the ls swap forum with no responses, hoping this is the right forum to find my answer.

Thanks in advance.