For that last, a sense of so long you have to wind your watch at least once before it's over -- a bit of folk etymology altering the original sense. The stem-winding watches invented in the mid-19th century was a big improvement over the key-wound watches of the previous century, given you no longer had to keep track of the key (usually by putting on your fob). Having such a state-of-the-art device was something to boast about, thus leading (by the end of the century) to the first-rate sense -- which seems to have been originally an Americanism but understood in England. The extension to specifically political speeches is purely an American extension of that concept (the idea that the speech winds up the enthusiasm of the audience is also folk etymology). The boring connotation is more recent.
Entry courtesy a New Yorker article on Donald Trump's campaign, which described a recent stump speech in Dallas as "a 70-minute stemwinder" -- apparently in the rousing sense, but the writer had enough ironic distance from his subject that the tedious sense cannot be ruled out as a sly undertone. Thus illustrating the dangers of using the word now -- two potential, contradictory meanings.