2005 Tahoe Z71 Fuel Gauge Wacky

[Huckster]

So my fuel gauge on my 2005 Tahoe Z71 has been acting up going to Empty and low fuel light coming on. It would vary with each restart. I replaced the fuel level sending unit in the tank and same thing. With the old unit it would not set the check engine light but the new one does. It is code P0463. I don't think its a stepper motor because the distance to empty is consistent with the gauge. As it varies the distance to empty goes up or down. The gallons used seems to be correct as this is how I know when to refuel. I don't want to pull the tank again to test with a volt meter but will if I have too. Any suggestions. I do have a spare cluster I can use to test.