A 2002 GMC truck driving down the road is crabbing down the road
Then something serious is broken, or the truck’s been hit and repaired badly.
and this could be dangerous to drive. Take it to a front end alignment place.
Measure the distance from the center of the front wheels to the center of the rear wheels and compare the left and right distance. If you have recently pulled a heavy trailer or had work done on the rear axle the alignment pin may be out of its hole or the pin may be broken.
Enter in your search engine: GM Truck Dog Walking.
And start reading.
Tester
Try “crabbing” and “going down the road at a crab angle” too. Those are the terms I’ve always used.
It might be a New England thing, I don’t know.
GM had problems with their vans doing this for a while too. They were coming out of the factory that way.
GM Tractors did the same thing, every other brand of truck had an adjustable torque arm locating the rear axle(s). Gm axles were located by the spring which depended on where the holes for the mount were drilled in the frame. Many Chevy and Gm tractors went down the road a little sideways. It nade them handle poorly in bad weather but the real killer was when you had to back the trailer into a tight space and you couldn’t because the trailes kept moving a little sideways as it backed up. Actually I have never liked anything GM made. I don’t have that feeling about any other manufacturer.
Has any steering or suspension components been replaced and/or has the truck been on the alignment rack lately?
Serious misadjustment of the tie rods while setting toe can result in crabbing; or tracking as I call it.
I’m voting that your rear axle has swiveled a little. I do not recommend checking the rear tires using the front tires as a reference because the slightest turn of the front wheels left or right moves them a lot more fore and aft.
A better reference point would be to crawl under the truck and measure from each side of the transmission cross member straight back to the axle housing. If one side is longer than the other, then the rear axle will have to be inspected closely and usually remounted with new hardware. This problem is aggravated if the truck has a lift kit in it.
I agree that the problemsis more than likely something has moved a bit or is damaged.
However, setting the track with the front toe adjustments is perfectly valid. I’ve done many alignments in this manner and was even advised to do this in a suspension school once. It’s not an issue.