TV picture pixelated after installing new Xfinity modem

My TV picture has been pixelated ever since I installed the new modem that Xfinity sent me. Streaming is fine, DVR records a good picture, and Wi-Fi is working. 

I checked all the cable connections, and they are all tight enough. I bypassed the signal splitter and put the cable feed directly into the X1 set top box, and that did not fix it. I still get a low signal reading for my TV input from Xfinity. 

I tried 4 times yesterday to post this issue on the Xfinity forum. Each time after I finished writing the explanation, I received an error message that my description had not posted. Hope you can help me with my TV. Thanks.