I agree that the most likely cause is the toe-in. Was the toe-in checkes after the 4" lift was installed? Changing the suspension height changes the toe-in. A 4" lift will result in about 1 to 1-1/2 inch of toe in when you should have about 1/8 inch. This will cause the tires to scrub wearing them out quickly.
It's too late to do anything about your front tires now. If they are really as bad as you describe, I'd just buy a new pair and get the alignment checked.
Regular rotation is very important also. Rotate every 3000 - 5000 miles. The more aggressive the tread, the more frequently you should rotate.