Prius pulling to the right

First, sorry for the wall of text.

I've got a 2006 with package 6 for about 1.5 years. It came with 92k miles and ran great. After about a year, i noticed a slight pull to the right, which got worse over time.

When i originally got the vehicle, the front driver's side tire had a bit of sidewall missing on the outside, presumably from curb action, and all tires were running just a bit low on tread, but still ok. When i started noticing the pull to the right, i checked wear on them all, and noticed the front passenger side tire was wore on the inside edge and metal was starting to show.

I found a used group of 3 of the same type tire (Uniroyal Tiger Paw), and put them on to temporarily remedy the wear issue.

The pulling didn't get better though, it got worse. After a while, i would need to hold the wheel about 5 degrees to the left with constant pressure to keep going straight, and if i let go, i'd be going towards a ditch within a couple of seconds, and i brought it to an alignment shop to get it aligned. I told them my issue was the vehicle pulled to the right quite noticeably and needed that remedied.

They rotated front tires and fixed the toe-in, of which the driver's side front toe was -0.18, front passenger toe was -0.12 and total toe was -0.30 and brought it to -0.06 and -0.04 respectively with -0.10 total toe. Strangely, the rear toe numbers were +0.09 and +0.24, but after front end alignment the rear numbers were +0.08 and +0.17. I asked them how the rear toe changed since they didn't touch it, and they informed me that rear toe was a relative measurement to the front. Since the front changed, the rear did in relation. Whatever.

This did not remedy the problem, as the vehicle still pulled to the right. I called them, and let them know of the situation and they asked if i could cross rotate the tires left to right and front to back. I did that, and it still pulled to the right.

They checked alignment again and front and rear were out of spec. Front started at -0.21 and +0.04 with -0.12 steer ahead, and rear was -0.02 and +0.37 and after alignment, front was +0.02 and +0.03 and rear was -0.08 and +0.38. The vehicle still pulls to the right. They mention that tires may be the culprit, even though i rotated front to back and left to right, and maybe i should get a shim kit.

Am i missing anything? Is it possible that the steering angle is off and it's causing the pull? Tires will be purchased within a month or so, and i'll get a shim set, but does anyone else have any idea on what's causing alignment to change so drastically? The vehicle hasn't been in an accident since i got it, and i don't drive it hard, and also haven't hit anything hard enough in any way that may affect the alignment that i could tell.

I've attached both alignment sheets.

 

Both pulling to the right and having to hold the wheel at about 5 degrees to the left.

I asked about loose parts, they said they didn't find any, and checked briefly myself while rotating tires and didn't notice any play.

While I'm going faster, it seems to need a little more pressure on the steering wheel to keep it straight, but that may be due to the extra speed? It doesn't like torque steer or anything, or pull harder when braking harder.
I did notice while at low speeds (not more so while braking) , the steering wheel moves toward the right a bit about once per rotation of the tire and keeps moving to the right a bit at a time until it's about 5 degrees to the right, but if i holds the wheel, it's not a noticeable shaking feeling thru the steering wheel.

 

Also, probably unrelated...
Shortly after the first alignment, after driving about 8 hours at highway speeds, against the wind, i got a p0420 code. I ran 2 bottles of techtron injector cleaner thru and the code disappeared.
While the code was on, i would randomly (not consistently) have issues with the cruise control. While at speed, it would hesitate and accelerate like it was losing power about 2-3x per second and sometimes for a few seconds at a time. It would accelerate hard then let off. If i used the accelerator manually, it would drive normally.
My first thought was the accelerator or brake pedal sensor. It's not occurring now, but it's a totally random thing, hopefully unrelated to my alignment problem.

 

Yeah, there aren't a lot of good options for alignment within 30 miles of me. They've done a very good job with all of my other vehicle's alignments, but who knows. Should i trust a firestone certified place?
I'm keeping tire pressure at 40, it was the first thing i checked.

i've also been reading if the rear beam setup isn't centered first, the whole alignment will be wrong