You will likely have to get in the habit of talking to the producers or at least the meat dept. peoples. I have a close relationship with the meat dept. people at all my local co-ops and specialty meat markets. They know I'm the 100% grass fed guy and not to try and sell me anything grain fed.
As for the last couple weeks/months finishing on grain, you can look up charts on the web that show what happens to the nutrient profile as you feed grains. It only takes a couple of weeks to ruin years worth of grass feeding. Annoyingly enough it takes a year or so to reverse it the other direction. I'm not sure exactly why this is, but the point is, the label should say 100% grass fed, if it doesn't, then there's a possibility that they were grain finished. Ask the meat department and don't quit until they convince you one way or the other. If they sound unsure, then they are unsure and you need to go over their heads.
Grain finished is that bad, I wouldn't touch it unless you have no other alternatives...<----- this is almost never the case.
You have to decide which veggies are good for you. Everyone is different, you'll have to find which ones give you energy/healing and which ones cause you digestive discomfort. Don't ever rule anything out, as you heal you may be able to digest things you couldn't earlier, so it's ok to try a vegetable again later even if it doesn't work for you now. No one can decide what is good for you, we can only give you some general guidelines and explain the fundamentals, then you have to choose the rest for yourself based on your results.
There's a lot to learn and it looks like you are on your way. Don't give up!
Look in to the weston A price foundation if you haven't already, they will explain what makes traditional foods, at least for livestock...ie ruminants eat grass/leaves only, fowl and pigs should get a variety of foods including meats/bugs/grass/seeds, etc...
To understand what I'm saying, a rattlesnake's natural diets is snakes, frogs, small rodents and rabbits. If you were raising snakes as livestock, you would want to buy the snakes at the grocery store that were eating these things, not snakes that were fed milk or tomatoes, that would be unnatural and produce unhealthy meat. Obviously you're not going to probably be buying snakes for food, this is just an example to see the underlying principle at work. Each animal, including us, has a range of natural foods that promote natural, healthful development. When that diet is deviated from, you begin to get dis-ease, both in the animal being fed that, and then the animals that eat them.