My commute is much the same as yours -- mostly high-speed (80-85 mph) left lane interstate driving, about 65 miles each way. I have 104,000 miles on my 2002 Corolla already!
Since I'm in the left lane almost all the time, I've found that the crown (the side to side slope) of the road causes the tires to wear oddly, and over time, a pull to the left exactly as you describe starts to develop. The wear on the tires from constantly correcting for the crown on the road looks like wear from misalignment after a while, even though the car is perfectly aligned.
In the world of motorcycling, a similar phenomenon is fairly familiar -- the left side of motorcycle tires always wears out first, ****uming you spend most of your time on two lane roads. In states with a lot of rainfall, they build the roads with more crown, and these problems are magnified.
The only solution I've found is high quality tires (the stock tires are complete garbage), frequently rotated side to side instead of just front to back.
I have about 4,000 miles on a set of Michelin X-Radials from CostCo, and they have maintained their "neutrality" far better than the stock Badyears or the Krappy Kellys that preceded them. They also have amazing grip in wet, dry, and snow conditions, along with an 80,000 mile warranty. At CostCo, a set of four was less than $300 out the door, about the same as cruddy house brand tires at the local tire shops. I'll have them rotated every 6,000 miles, as recommended by Michelin.
Your dealer may be reluctant to rotate side to side, since the manual calls for front-to back rotation. There's an old mechanic's tale that it's dangerous to rotate side to side, based on belt failures of early radials back in the 1970s. It's not an issue with modern tires, but many mechanics, being gullible and rather slow-witted, still believe and pass on what their uncles told them years ago.
Although you probably don't want to replace the stock tires so soon, it's worth considering. You'll be much safer through the coming winter (Toyota inexplicably mounts really awful tires at the factory -- almost anything has far better grip) and you'll most likely banish the pulling. If you spend a lot of time in your Corolla, high quality tires are worth every single penny.