The car has mild torque steer, maybe more than I realize, but I've been driving it so long, that maybe I don't notice any longer.

What I will describe below is NOT Torque Steer. I'll provide my attempt at defining torque steer to clarify.
Torque steer occurs when you are accelerating. In a FWD vehicle, the torque produced from the engine, will force the steering to pull in one direction or the other. On any given vehicle, the pull should be in the same direction each time you accelerate. Also the torque will remain relatively constant throughout the acceleration process (it may increase or decrease depending on the load produced by the engine).

Description of the problem
I recently changed the high pressure power steering hose in my 2002 I35, and then rotated the tires. I now have a noticeable pull/jerk on the steering wheel when I accelerate from a low speed (i.e. 15 to 45 mph). The wheel only pulls for a brief time (fraction of a second) and then the car continues in its normal trajectory. It feels as if you are going to be pulled off the road when it happens, but it quickly finds the path and can easily be steered straight. I can get the same type of movement from the steering wheel, under very mild acceleration, it if is timed with a gear change.

The same will happen if you are accelerating hard and then you quickly release your foot from the gas. So, under heavy acceleration, there is not much torque steer, the car accelerates straight, but then when you let your foot off the gas the wheel the car will noticeably dive to one side (I think it was to the right) and then straighten out. It is easiest to reproduce if the foot is removed from the accerator when the car is just shifting into 3rd. This seems to be longer change in my car, and the combined effect of lifting off the gas while the trans is shifting to 3rd will cause the wheel to jerk to the left.

The first time I felt this, I thought it was going to take me off the road. It did this once in a turn, and that was a bit unnerving too.

I can reproduce this at will.

What could be causing this?

Is it possible that the aftermarket high pressure steering hose doesn't work as well as the OEM; and that somehow the pressure in the steering is surging and causing the pull?

Or could it be that a motor mount is going bad, and that the motor is shifting, causing this apparent steering issue?

Or is there some component in the suspension that I should check? Struts, ball joints, bushings?

Thanks for any help that you can provide.

Power steering pump could be a possibility. How about you un-rotate the tires back the way they were and validate it's not a tire issue (I doubt it is). If the problem was not there before you changed the power steering hose and you have validate it has nothing to do with the tire rotation then I would say the issue is with the steering system and I would look there first.