ALIGNMENT ?? - 2003 Impala 3.4V6

I recently upgraded to H-rated tires of OEM size for my Impala and had
4whl alignment done as a package at a local Town Fair.

The improvement from S-rated to H-rated was noticeable, particularly in
steering response. No more squeal in turns, and a firmer ride.
Unfortunately, the car "seemed" to exhibit some pull to the left, which
I brought the car back for the next week.

My sales rep reviewed the alignment printout which showed everything to
be pretty much within manufacturer's spec window, but proceeded to rack
up my car for an adjustment. And actually, the conditions that would
contribute to a left-pull: more positive camber on the left, less
positive caster on the left, were not the case!

Afterwards, I was handed a new print out, which showed my caster to be
just outside the manufacturer's window, but all other measurements
within spec. Caster for the '03 Impala should be +2.7 <> +3.7 deg, but
mine was +2.5L/+2.6R. I asked how the caster got to be so out of spec
and will it effect my driveablity, the sales guy said, the other
adjustments affect caster, and, no, it shouldn't effect driveablity.

Once back on the road, the left pull was gone, but now the car exhibits
little or no "center" feel to it. Steering wheel return after a turn
is not nearly as nimble, and I often must correct slightly one I'm on
the road I turned on to. And even at highway speeds, I have to guide
the car to keep it in the lane I'm in.

If what the sales rep said is true, what other adjustments can have an
effect on the Impala caster, which itself is not adjustable? And what
should I have them do to get the caster closer to GM's +3.2 suggested
spec?

Thanks in advance,

-ChrisCoaster