How are the rear tires? I don't know too much about 2wd's so this is all I can ask...Mark Also check the spring u-bolts to see if the rear axle has shifted, this is a shot in the dark, which is also my favorite Peter Sellers movie...

 

Have someone drive behind you and see if the truck is "crab tracking".

I've seen alignment shops do shoddy work, or do it with uneven tire wear. Not good either way.

 

Did they give you a printout from the alignment? If you posted it here, somebody may be able to see something that was missed. If there's a thrust angle on the rear axle, it can cause a pull. I would also try swapping the front tires left to right. I know they're new, but I have seen new tires pull, more than once. Never with Michelins though, incidentally.
Generally, if it's a pull to the left, it's usually a more obvious problem than a pull to the right. If it's a problem with alignment angles, for example, it has to be out quite a bit more to overcome road crown and pull the vehicle left.