good tires

99 expedition have Goodyear HP on now. They have small holes?? wart looking things in between the tire treads. Goodyear says they are all used up and need replacement 40K on them. But they wont or can't explain what caused the warts. They still have good tread. Any suggestions on a good tire. Their tires still only have a 35/45K warranty. God I love my Michilens 95/102K on them and still sold them as used.