1991 is also cast, not forged, and more closely resembles a 1911A1 from the good old days (no angled serrations, relief cut under trigger guard, beavertail, flat top slide).
All Colt 1911 types (including the 1991), save special models and Gold Cup, have a nylon trigger.
The three dot sights are a good feature to look for and weren't standard on the 1991.
Colt's machining sucks quite often and the slide will seem lopsided due to uneven grinding of the flats of the slide. Doesn't mtter what model either, cheap or expensive. Is it any wonder they're hurting?