Post alignment specs. Any good?

On a level road with no crown you'd ideally want to have equal caster left and right but often alignments will have a bit of road crown compensation built in to to the alignment. The rule of thumb is that, with all other things being equal, the vehicle will pull toward the side with lower caster, so if you're driving on a flat, non-crowned road, the pull to the left would be normal but would disappear on a crowned road.

That being said, without seeing all of the numbers, it could still be that your rear axle is in very slightly crooked, and it doesn't take much, causing a slight pull. And since these caster numbers are very low already, and higher degrees of positive caster are very helpful in how your vehicle tracks in a straight line, it's like that with such low caster numbers that the offset between left and right is causing an overcompensation for road crown and contributing to your pull. After you put in your new control arms you should be able to get between three and four degrees of positive caster and you can ask them to either make the caster equal or only, say, two or three tenths of a degree less on the driver's side instead the full half degree you have now.

For comparison, my old 911 is set to run nearly six degrees of positive caster, which is why it tracks straight as an arrow and the wheel just snaps back to center when you let it go from a corner. And remember that when you have positive caster that the whole suspension assembly is leaning back slightly, meaning that the top of the strut assembly is going to be two or three or four degrees (which is the caster) toward the rear from the base of the strut and when you turn the steering wheel with positive caster, you're actually slightly lifting the front end of the car or truck. More positive caster and you're lifting it more as you turn the wheels, which in turn is what causes the wheel to want to return to center when you let it go.

And there is a very slight chance that a bad tire could cause a pull but my guess is that once you put in the new parts and take it to a good alignment shop, you're going to be much happier.

 

Great information and explanation! Thanks for posting this!

A tech did mention road crown compensation, but the truck will pull left even on moderately crowned road. I'm also on brand new tires and already I tried rotating (side to side), but that didn't make a difference. I'm eager to see what we can do with the new UCAs. Thanks again for the info!

To the OP, sorry for the thread hijack!