E150 Tracts to Left

My E150 XLT passenger van recently began to 'track' VERY slightly to the left as I drive. Seems like I am always adjusting the steering wheel to straighten it out. This all seemed to start when I rotated the tires. I have two year old goodyear radials ( 30K ). I did 'cross' the tires so that, for example, the former left tire is now the right front. Also, the brakes are only a few years old and when I stop abruptly, I sense no track to the left....so I suspect it is not the brakes.

Thoughts? Ideas for diagnosing?

Tire pressure is my first thought. Tire size is the second - are all 4 the same size and tread? Since this only started happening after the tire rotation, it pretty much has to be a tire issue.

Tire pressure is my first thought. Tire size is the second - are all 4 the same size and tread? Since this only started happening after the tire rotation, it pretty much has to be a tire issue.
sounds like a belt issue,, where as in the rear you would think that you would feel a shimmie, but if its off a little you will feel it more when the tiers are in the front

Do you have aluminum wheels? Swap the front two wheels with the back two and see if it goes away.