You are correct. All three words are pronounced with a "t" sound at the end.

Yes - the final 'd' is unvoiced, as if it were a 't' sound. This would be the same in any native-speaker accent. I'm not sure why you specified 'American' pronunciation : the variety of English makes no difference here.

You are correct. "Clashed" is pronounced as one syllable, "outclassed" is pronounced as two. This is usually true in modern English for words ending in "-ed." I can't think of an exception offhand. Wait, I can. "wicked," meaning evil, is pronounced with a voiced "-ed", almost like "wicket," not like "wick't." UNIMPORTANT: In the English of a few centuries ago it is clear from the meter that the -ed WAS pronounced voiced, as an separate syllable. Sometimes there is even an accent mark over the "e" to make that clear. And it is sometimes written with an apostrophe instead of the "e" to make it clear that it is NOT voiced. In a famous Bible passage, "Blessed are the meek: for they shall inherit the earth," it is traditional to read "Blessed" as two syllables. But someone using it in normal speech would pronounce it as "blest." And it is actually spelled that way in a famous poem, Edward FitzGerald's English translation of the Rubaiyat of Omar Khayyam. In a poem, "Sea Dreams," by Tennyson, published around 1864, I find "the brittle fleet... near'd, Touch'd, clink'd, and clash'd, and vanish'd, and I woke." So, somebody thought it was necessary to put in apostrophes to make the pronunciation clear, but it must have been an acceptable pronunciation even then. Today, those are just the way "neared," "touched," "clinked," "clashed," and "vanished" are always pronounced and no apostrophe would ever be used.