One of the first things we learn when we decide to do a steroid cycle is that injectable steroids can hurt! This is especially true with muscles that are not used to having steroids injected into them, AKA virgin muscle. Over time, the pain becomes easier to deal with. Some shots are going to hurt more than others and some brands are going to be more painful than others. Geneza using very thin carrier oils that absorb fast and quickly into the muscle. Believe it or not, Geneza is one of the more pain free brands out there now days, IMO. No matter what you do, certain factors are going to cause more discomfort. Fast acting test, like test prop, is commonly considered to be one of the worst steroids for injection pain. For this reason, I don't reccomend prop to new users. What happens is, the fast acting ester breaks down faster than the test can be passed into the blood stream, leaving the hormone sitting in the muscle. After a couple days of pain, I find that working the muscle, bringing in fresh blood, tends to help speed up the process of breaking down and carrying away the remaining hormone.

The reason that your T400 is painful may be totally different. Personally, I found that GP T400 isn't painful for me. I never injected it on it's own though. I've mixed it with another steroid when I've used it. 400mg is a lot of hormone to disolve into 1ml of oil. If you'll notice, big pharma doesn't make test any higher than 250mg. It may require more solvents to keep 400mg from crashing (re-crystalizing) and these solvents can make a shot more painful. Even if they have the solvents low, it can still cause quite a bite. I would stay away from using T400 in small muscle groups. Something like a delt doesnt have as much room as a glute and is more likely to become irritated. Mixing it with a less painful steroid like EQ will also help to reduce pain. If you aren't running anything else on this cycle and find that the shots are not setting right, you can purchase sterile cottonseed oil online to mix and cut the mg's down. I would mix at a 1 to 1 ratio and see how you respond to that. 

If the pain last longer than a wk and doesn't seem to be getting any better, or if you develop a fever, you may want to have it looked at by a Dr. Even with the most sterile injection technique, it is still possible to get an infection. Just the irritation of too much hormone in one spot can be enough to trigger your body to attack it as if it were an infection