Just in case someone else is experiencing slow response on Channels playback, especially when skipping back or forward, it may be a FireTV stick problem.
All of a sudden I started experiencing very slow start-up times after skipping back/forward. I did the DVR speedtest within the Channels app and was getting only 30mbps. In FireTV I disconnected/reconnected to the network and improved to 300mbps. But it would only stay at 300 for about 20 minutes. Then I would see delays again. Speedtest was back at 30mpbs. My FireTV stick was a little less than a year old and was within the replacement window. Got a replacement from Amazon.
The new stick is working fine. No reduction in download speed.