2011 Kenworth T800 power steering issue

Hey y'all,

So we have a 2011 Kenworth T800 with a Cummins ISX 11.9 engine. A few weeks ago, the driver was dropping off a container at a residence, and the steering locked up on the truck as he was leaving on the road. He was able to get it free and parked it and we were called out, and decided to tow the truck back because we felt it would be unsafe.

Someone had decided just to change out the power steering pump, which we did to no resolve. They changed all the lines, ended up changing both gear boxes, flushed the fluid many times, bleed the air put of the system many times, bypassed the cooler, bypassed both steel lines going to the assist on the passenger side. The kingpins seem good, replaced the drag links snd are in-time, replaced the power steering filter; etc, etc..

While in the air, the steering feels good, on the ground it will feel okay until the fluid starts to heat up, then it is impossible to turn left or right.

We had pressure tested the supply from the pump, and it reads 1,100 or so psi while turning left pr right, but when attached to either line on the steering assist, it only registers pressure while turning to the right. Coincidentally the lines stay cool, whereas on the driver side everything heats up, including the cooler. It seems like we have some kind of restriction from left to right, but everything we have tried wouldn't point to that as an issue.

I suppose (if you have been able to follow along thus far) I'm more or less looking for any advice or any ideas with this issue.

Thanks for those that have read this and may offer your know how to assist us!