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What speed internet service did you buy?
Which Telus modem model do you have?
How far is the Chromecast device from the modem?
What numbers do you get at SpeedTest.net?
I find that Chromecasting a tab has major stuttering/lag issues but native casting, for example from YouTube, doesn't usually have such issues.
If you have slower computer then it can't do the on-the-fly conversion of the tab into video content fast enough and you get lag.
Shaw would have the same.
@telusbabe based on @SunDog comment, and the speeds you describe, the problem does not appear to be with your connection, as even 5 - 6 Mbps to your Chrome device should give clean video. I suggest looking in the direction mentioned by SunDog.