I had the same problem when I started painting my dinning room red. It was a semi-gloss latex (Ralph Lauren) and it showed roller and cut in marks. When working with Semi-gloss latex, you really can't let the paint dry. It needs to stay went to properly blend in. I solved this by buying a Wagner Pro-sprayer. Yeah, it took 4 hours to prep the room, ceiling, floors, wood work and stairs, but it was only 1 1/2 hours to paint and the room is beautiful. No lines, no marks, just a great finish. To speed up the prep work, go to Walmart (best price) and get some 3' plastic sheeting that already has adhesive tape. Blue tape your ceiling, for the straight lines, then put the pre-taped plastic sheeting up to cover about 3' in on the ceiling. Make sure the plastic overlaps well. Do the same around any molding and woodwork. Get longer plastic to cover windows and doors. There is also a 5' pre-taped plastic that works well. Take large tarps or plastic and cover the furniture and all of the floors. Yes the prepwork is long, but spraying is a breeze. I found that using the tube directly to the paint cans was easiest, as sprayers have a tendency to spit when they are low on paint. Wagner comes with both an attachable jug, or a long tub that you can just plop right in the paint can. Go in gentle strokes left to right, starting at the top of the wall down. Make sure that you have protective clothing, long sleeves, long pants, hat, gloves, goggles and a respirator as the overspray and paint mist does get pretty heavy. Ventilate the place well. While it seems like a lot, the end results are well worth it.