not getting 1080i signal

I have two Sony TVs, both connected to my Uverse box via HDMI: on one, I am getting a 1080i signal but the other is only 760p. On that other TV, I do get 1080i when I use my outside antenna. How do I get a 1080i signal on that TV via the Uverse box? I see a definite picture improvement with the 1080i.