Just bought the new kickr core 2c1f162 and set it up on Zwift. When I try it out it’s showing my speed to be at least 3-4 mph higher than what I’d expect. I’ve tried unplugging, re-pairing, doing multiple spin downs and no luck. I double checked it on the wahoo fitness app which seems to be tracking accurately. What do I do!
Note: also used the kickr and a separate cadence sensor for cadence
You can’t expect Zwift speeds to be the same as IRL. Game physics might get you close, but it is still going to be different.
Might be helpful.
I’m about the same amount faster on Zwift than IRL too. Some other apps, such as FulGaz, have settings for tweaking your drag and rolling resistance coefficients so your speed is more realistic. I think it would be a useful addition to Zwift, but for now I just enjoy being faster for no extra effort 
Others who’ve commented here seem to have got you covered. In my experience, you’ll want to focus mostly on your power (e.g. watts) readings in-game. If the power readings look correct to you, then the speed is almost certainly what it should be in most cases.
Unfortunately the power is off as well. And, the Wahoo app is now showing the same thing - power around 50-100 and somehow going 16-19mph. I reached out to Wahoo and they told me to do a factory spin down but it didn’t work. Hoping they’ll come back with another solution
Understood and yes, if the power readings being incorrect is an issue that’s also happening in the Wahoo app despite your efforts to calibrate and update the KICKR Core firmware, it would appear to be an issue with your trainer as opposed to being an issue with Zwift. If you’re already in contact with Wahoo Support, it seems that’s the best avenue for help at this time.