Casey,
It sounds like your lo is ready to move to 4 hour EASY. Are you still on 3 hours? My DD did this when she was around 4 months... just screamed when we put her in her crib... we literally had to pin her down to the crib with our body and limbs AND pat her before she could settle down and fall asleep. We also, did not swaddle Arwyn from early on... I know you no longer swaddle Katie (read your other post). What I did though, was what I called "pseudo-swaddle". I picked Arwyn up (over my shoulder hold) and placed a blanket over her and then tucked the left and right ends between me and her. She then, can't thrash her hands around while I am holding her.
You are doing everything right... from you post, I can tell that you are doing everything you can, to get Katie to sleep independently. Give yourself a break too... work on one thing at a time. Pick the nap you want to devote your 100% to and then do what you need to do for the other ones. When you see success, and you will... then pick another one.
PU/PD does work... I have done it myself to teach independent sleep and to extend naps. I am now, doing PD to teach independent sleep, yet again, due to loads of accidental parenting. So... stick with it Casey... EASY isn't always easy but it is worth it. If you put in the time now, it will pay off. It is frustrating while Katie is getting used to it but she will.
You are doing great! Hang in there... there is an end in sight... you may have to do alot of searching, but it is there. Count every little success as a step towards your goal!
Loads of {{{{{HUGS}}}}} to you.