I took them back to the tire shop, thinking they were improperly
balanced.  Multiple times.  Eventually, a half deaf kid that gave a
sh.t took the time to figure out why I had been in there so often, and
when he found the reason, he brought me out to the balancer to show
me.  I saw first hand that the wheels weren't round, in turn, as they
spun on the balancer without a tire on them.

as others have said, it's probably not bent wheels.

that said, you need to know the rim width, the bolt spacing, and the
offset.  None of which you'll know for sure without a measuring tape.
You don't even have to take the tire off to that.

Ray

Thankyou for all the suggestions.

Regarding bent or not, each of the four wheels have a 'flat spot' on the
inside flange- when the tire guy stopped the wheel from turning, it was
pretty distinctive.  There's a big 1" bare scuff in the rim where it
looks like something metal exerted force on it and pushed it in ("in" as
in perpendicular to the axle).  There is also a corresponding mark on the
inside of the wheel itself (the part that is horizontal when on the
vehicle).  On all four, the outside flange is fine.

The truck rolled fine and smooth with the old Firestones on it (almost
100K miles on them, no less).  After getting 4 new tires put on, I
noticed a 'wobble' leaving the parking lot, but it was cold out, and I
figured the tires were stiff and misshapen from sitting.  It smoothed out
a little on the street (40mph).  That evening I found that at freeway
speeds it is like sitting on a washing machine during spin cycle.  In wet
road conditions the vehicle is actually unstable (like driving too fast
on a washboarded gravel road). I took it back to them three times to have
them rebalance the tires, and nothing changed.  

I took it to a different shop to be rebalanced (a local reputable place
that unfortunately no longer sells new tires, but the old guy that owns
it knows his stuff.).  They didn't notice the wheels being bent
(strangely), but instead claimed that one of the tires was defective.  
They also questioned the large weights that were put on by the other
shop.  It shook just the same after that.

I took it to the original shop a fourth time. I told them what the 2nd
shop had stated, and they replied by telling me that my warranty is now
void because someone else touched them.  In any event, they still brought
it in to look at it.  The tech said "yeah, this tire has a 'hop' in it.  
That will settle down in a few thousand miles".  I called bullshit, I
demanded to speak to a manager, and did, and he had the deaf kid look at
my tires.  He's the one that pulled the tires off and showed me the
damage on my wheels.

So there it is.  I haven't been back since.

-phaeton