I'm going to guess that you cooked a flat since it was 4.5 pounds. A properly cooked flat, once sliced, will dry out. That's just the way of that piece of meat. It is a lean muscle with lots of connective tissue, so the only moisture it gets is from the connective tissue converting into gelatin, and as it cools this hardens and it seems a bit tougher and drier than when it was still hot.
What you want in a brisket is great flavor and tenderness, which it sounds like you got, so congrats on making an excellent brisket flat. Some people try for a loooong time with bad results, so you have reason to be proud.
Now a whole brisket (or packer) contains both the flat and another piece called the point with a thick layer of fat between them, and is much larger, usually found beginning around 10 pounds and up. This meat in the point stays juicy after it is sliced (actually it's usually chopped) because of the high fat content. This fat will stay moist even while it is still cooling down, up until the point it is basically fully cooled to room temp or chilled in the fridge. This fat also has tremendous flavor, for the same reasons the crispy soft cooked fat on a steak tastes so good. So the point is really where it's at (in my opinion, and many others).
I never see just a point for sale, except in the case of packaged corned beef, I usually see either corned beef flats or points available for sale. So the only reasonable way to get a point without placing a custom order is to buy a whole brisket to get one.
Anyhow, I just said a lot, you just read a lot (if you're still awake), and all I have told you is that it sounds like you did good and that flat turned out just fine. Next time you might try a whole brisket and see how you like that.
As for the pink, that pink should only be around the outer edge of the meat, and as others have mentioned is the smoke ring. This is formed from the smoke when cooking. It is not pink from being cooked less, but pink from being cured, much like how ham or corned beef are pink. The smoke actually cures the outer portion of the meat as it cooks turning that outer edge pink.
A brisket is not done until it is usually 185 or higher. If you want to use temp as a guide think 195-200. However, I do NOT recommend judging a briskets doneness by temp, but by feel. Not all briskets get tender at the same temp. They get tender when all of the connective tissue has converted to gelatin which is a function of the quantity of connective tissue, not the temp of the meat. As you cook more briskets, you will start to recognize when they are done. I do a probe test, which is to stick a probe in both the flat and the point. When the probe goes in with no resistance into both pieces, it is done. Probe the flat in a couple spots too because many times the outer part of the flat is done before the part in the center where it is hiding under the point.
Good luck on your future briskets! Keep up with these guys on the forums, you will get tons of advice and learn YOUR way to make the best brisket. Sometimes other people find a way that works for them that is different from others. Stick with what you like. Just make sure it's tender first, no matter WHAT method you choose, that sucker needs to be tender to be good.