Gas guage

[Razr]

I just had my fuel tank sending installed and hooked up to the gas guage on the dash. There is one problem though when I let the truck sit over night and then in the morning use it the gas doesn't read. But then If I let the truck sit and use it in the afternoon it reads the gas what is the problem. When I turn it on the gas doesn't work then if I let it sit for 3 hrs or so it works.