First and of utmost Importance, when we speak of "low and slow" cooking, what we are trying to do is warm up the inside of a steak or roast without overcooking the outside. This can only be done with relatively low heat and a longer cooking period. Grass-fed meat tastes best and is more tender when raw (as in steak tartar from a washed steak or a top quality boneless roast) or from very rare to rare when cooked. Secondly all meats are more tender when sliced properly.
Many people have the idea that meat must be cooked until it turns brown on the inside. But that is nonsense. Please do not approach 100% grass-fed steaks that way. A correctly cooked steak is juicy and limber. Cooking meat until "no blood runs" is another one of those things people do to ruin a perfectly good cut of meat. Meat is 70% water and, yes, the water will have some blood cells in it. But it is not anything like blood from a major vein. So don't get the willies when the juice is a little red. When the water is gone (no juice) you have made jerky.
As mentioned above, all meats are 70% water. When steaks and high quality boneless roasts are cooked beyond rare, they are being dried out excessively. Once again, this is how you make jerky. Jerky is merely dehydrated meat. Jerky is tough and, without spices, not very palatable. So we highly recommend against overcooking grass-fed meats.
Rare cannot be determined by the "redness" of the meat. Rare is determined by the internal temperature of the meat. A medium-rare steak is cooked to an internal temperature of 140ºF and is barely limber when removed from the grill. Rare is 120ºF or less and quite limber. Sometimes it takes us 25 minutes of indirect heat to warm a steak up to rare. This is low and slow cooking at its best. Over direct heat on even the lowest setting, 10 minutes can be too long. Always keep in mind that grass-fed steaks should still be very red and juicy inside when cooked properly. A grass-fed steak cooked until it is "well done" becomes dry and extremely tough--not so good for eating but possibly good for shoe leather!
When we fire up our gas grill, we immediately set the knobs to their lowest settings. Then we put the steaks on the cold portion of the grill. We call that "cooking." The grill warms up slowly, but "slowly" depends on the ambient temperature. We first turn the steak after about 5 minutes. The "hot" side of the steak will look nearly like it did when it was first put on the grill. The next turn may be in another 5 minutes. This time the steak looks like it is starting to "cook." If the temperature inside the grill is pushing much above 200ºF, we must shut down some of the burners. We want the grill's temperature to be no higher than 200ºF. Depending on various factors (steak thickness, winter or summer grilling, the wind, fresh gas tank or nearly empty gas tank) it may take another 7 to 12 minutes or more to finish warming up ("cooking") the steaks when using indirect heat. Be careful with direct heat because most grills set on low can overcook a steak in 10 minutes or 5 minutes per side. A limber steak is a tender palatable steak; a stiff steak has been "killed."