@hopefaith I am sorry you are having such a tough time. From what I understand, getting a straight leg is tougher than getting it to bend. As for ROM I
don't think it is what they get all the time. I know for my husband it is what he was able to do really pushing himself, not what it does naturally. He has a lot of 2 steps forward, 1 step back times. He gets a lot of the 'tight band' feeling, expecially in the morning. His PT taught him to lean on the kitchen counter with the leg out behind him and gently stretch it out, and then bring it forward (with the other leg out behind) and gently bend it. This seems to help with the stiffness.
From what I read on a lot of different forums, depression is a part of TKR. I believe it is because everyone gets tired of feeling helpless and in some ways useless because of their limited abilities while they heal. From what I understand that feeling goes away as you start to heal. Most everyone hits 'walls', stalls out, and has set backs. I've seen it in my husband. His way of coping is if he has a bad day, he doesn't do as much. He tries to keep mind busy so he doesn't dwell on it so much -he does crosswords, builds model cars (which he hasn't done in forever), and watches movies on Netflix.
Remember everyone heals at a different rate, it has a lot of variables including how much manipulating they had to do to get your leg straight. Your muscles have a memory and if you walked 'weird' for a long time they want to go back to that way of walking, so they are fighting your new straighter leg.
I quess what I am trying to say is 'hang in there'- this too will pass.