Your TV is doing all the work to decode or get around what any black boxes would once activate and thus allow media stream from the source. Since, you state you don't have that your TV has to do it and that takes time. -OR- copyright scheme is active and has to be reset everytime you change CHs. otherwise, you wouldn't see anything. Either that or some decoding is being done somewhere on your connection prior to your TV, I just can't see free cable otherwise unless provided as a package service in the home owners area or similar. Basic service included could be part of the package setup and isn't getting the full blown access of the best signal. I do exclude any outside forces of the connection itself. I just get the feeling that decoding is involved and causing the lag, maybe HDCP as well.

Since this is a new TV, maybe configuring of the TV itself could be a problem. TV setups has gotten so dang complicated, so be sure that is correct. AND yes, different TV do this slightly different, so review your owners manual for clues. You may want to checkout the Roku 3 as something that could help.

tada -----Willy Happy