If you are responding to my shots, thanks!

I took a look at your shot and I see several areas that could be improved.

Movement. It is fine to pan which you seemed to have done a bit. The background is slightly more blurred than the bike and rider. Your results will improve tremendously over time. At 1/400 second you should have been able to track the rider and get him in focus and without blur using a lens with a 46mm equivalent field of view. But your working distance of about 12 ft makes it harder, since the amount the rider moves through the scene (and across the sensor), is greater when you are that close, compared to say, 20 ft with no change in focal length. However, when you are further away, most will select a longer focal length, increasing the magnification of the subject, and along with it, the opportunity for blur - so the answer here is to practice panning. You can also just freeze everything by using a fast shutter speed, as I did with some of the images I posted, for a completely different look. I personally like a little bit of background blur with a properly tracked, in-focus and not blurred main subject, at least most of the time. Acquiring good panning skills will give you more options.

Exposure. As others have mentioned, allowing the camera to adjust exposure without your input can result in uneven results. By and large, you can read the exposure with a separate meter or the one in the camera, and the exposure should work for all conditions unless the rider is moving between light and shadow. Under those circumstances you may not have a choice but to allow the camera to adjust exposure, at least in the beginning. I control exposure and adjust on the fly (been doing it that way for 50 yrs) so I don't expect that you will be able to master this at first, but it may be something to strive for down the road. My 18 yr old son, who took the wheelie shot, has good control over exposure, so it is achievable. I shoot manual, and use the camera's spot meter mode to find the brightest highlight in which I want to retain detail. Meters are calibrated to provide a middle grey tone, so if you take the meter's reading as gospel, whatever you point it at will be perfectly exposed as gray. So, if the camera says F8 at 1/1250, I would expose at F5.6, so that the highlight area that was metered can appear brighter than middle gray, but not so bright that I lose detail, as you did on the front fairing and the tops of the saddlebags of the bike. This may be counter intuitive if you are using a camera picture mode, like sports. When you dial in +2/3 stop exposure compensation and you are in evaluative or matrix (Nikon-speak) mode, it will make the entire image bright. But the key is that when you use spot meter, you are being quite selective by reading the highlights - and setting your exposure based on that, rather than reading all the tones and letting the camera decide. It is more accurate to read the highlights, since that is information that will be lost if your exposure is too high. The best way to do this in the field is to turn your camera's Highlight Alert on, so overexposed highlights will blink when you review the image, and look at the histogram - what you are looking for in the histogram is that none, or very little of the image data (the graph) touches the right edge. This is covered on Page 272 in the camera manual. It's ok to have the reflections on the chrome appear bright and without detail.

Focus. - In addition to blur from motion, The rider is not in focus. At F4, your depth of field at 12 ft with a 29mm lens is a very generous 9 ft. But if your subject is moving, there is always a risk that the camera can focus on something other than the subject, or because he was moving fast, the camera may not have had enough time to focus before you pressed the shutter. I am not that familiar with the T5i to advise you on what the best AF settings are.

Post Processing. Like it or not, most, if not all images can be improved upon with careful post processing. I shoot everything raw, and adjust what I need to in post processing using Lightroom and Photoshop.

This article may help you get a better understanding:

https://www.slrlounge.com/freezing-motion-with-high-shutter-speed/