I traded my original Mass Effect 2 and 3 for a friends his new WWE 13 and ended up buying the Mass Effect Trilogy for a great price (Disc over digital EVERY time for me, looking at you Mass Effect 1)...
Anyways long story short, I bought the trilogy expecting bugs to be ironed out on the new discs as less has to be loaded off the hard drive and it suffers from all the same problems! I've been playing the latest Citadel DLC and the framerate at times is downright criminal!
I've seen the game run on 360 and it doesn't suffer from the same amount of issues at all!
Really annoying as I've always thought PS3 to be the more powerful console of the two!
I had a really similar issue with Mass Effect 3. It started off with a little lag, then it would take longer for certain environments to load (Citadel II, certain floors on the Normandy)
It only froze once during a cutscene in which I had to restart the system, but then got through it no problem the second try.
It wasn't until the very end of the game when I had only about an hour left that the game went to a full on black screen and I could not get past this one scene no matter what.
Right now I deleted all the game data and am reinstalling it to see if there was any corrupt data on my hard drive.