Nissan: '96 Pathfinder: cupping wear on new front tires

I've seen some past posts in this group regarding recommended tires
for the Pathfinder. Based on what I had seen here and researched
through manufacturer literature, I came to the conclusion to purchase
a set of Michelin Cross Terrains for my PF (at Discount Tire Co.). I
was extremely pleased with them compared to my Mich. LTX A/Ts that
were on there when I bough it. (Yeah, I know those ones are more for
off-road and will have more road noise.)

Anyways, here is my main question: what would be causing the cupping
wear on my front tires? I have about 4500 miles on them and plan to
take it in this week for a rotation, but would like some ideas as to
what may be causing the problem before I take it in. Here is some
additional info about my PF:

1996 SE with 137k miles, adjustable shocks/struts were replaced with
OE adj. shocks/struts at 119k (most of the time I use the comfort
suspension mode), the upper and lower control arm bushings in the rear
were replaced and 4-wheel alignment was performed around 132k
(shortly before buying the new tires so that I could fix the "shimmy"
problem).

Thanks for any comments/opinions!

Randy.

Randy Schuster wrote: 
After rereading your original post, I want to point out that some tires
are more susceptible to cupping than others. My memory of the Cross
Terrains is that they have larger tread blocks than the LTX's.
Therefore, I would expect more cupping, or quicker cupping, than what
you (and I) experience with the LTX's. Maybe a rotation at 4,000 isn't
a bad idea with the Cross Terrains.