gas gauge stuck on empty

[amikk97]

hello all,
I just replaced my fuel sending unit in my 87 sierra 1500. I put in a brand new sending unit and when I was done, I added about 3 gallons of gas to the tank which was pretty much empty. i turned the key to the on position and could hear the pump priming, however the needle went all the way over to empty (it was stuck past full position since my old sending unit was bad) and it hasn't moved since. i added about 2 more gallons and it hasn't budged one bit. my truck starts and runs and drives fine. I tried rocking the truck back and forth to see if i could get the float to move, and i could hear the gas splashing around, but still nothing on the gauge. ive looked over all the connections and they all seem snug. any know whats going on here? please help