Rack and pinion

Do you mean as in looking at them from in front or in back? They lean to the left or right? Can you move them there by hand or only when turning the steering wheel?

I'm trying to figure what you had apart that can cause that. If the two lower bolts on the struts are loose, that will let the tires tilt in and out on top, but because of the steering geometry, it will also cause them to turn left and right at the same time.

Did you lower the cross member to gain access to the rack? Any chance you forgot to tighten it? It's also critical that it be bolted back in exactly the same location as it was or you will have a severe handling problem even after it's aligned.

What else did you have apart to replace the rack? Has it been aligned yet? Toe is going to have to be adjusted. If that is off enough it will make the tires walk away from or toward each other. Come to think of it, that's probably all that's wrong. The clue is the steering wheel will be off-center too.

Usually that's not a fuel supply problem, at least not directly. This is more typical of an electrical problem. More specifically, look for loose or corroded terminals in an electrical connector or wires that are rubbed through. The connectors will be between the body and engine where the rocking of the engine tugs on them. The wires often rub through on the body, also from the engine rocking, or they can by laying on a sharp metal bracket on the engine.

If the problem is related to a sensor, there may be a diagnostic fault code stored in the Engine Computer although GM has an unusual strategy where the computer watches a problem for a while before it sets a code. Check for codes anyway, even if the Check Engine light didn't turn on. The light is only required to turn on when the detected problem could have an adverse effect on tail pipe emissions.

If there are no fault codes, the best approach is to use a scanner that can display live data on a test drive. Many scanners have a record feature that will record sensor information when the problem occurs. Because the data travels through the scanner's memory, the recording actually starts a couple of seconds before the button is pressed.

If the engine sputters as it dies over a period of a few seconds, fuel pressure may be dropping off. If it dies instantly, similar to turning the ignition switch off, a loss of spark problem is more likely.