i have a 2000 chevy blazer 4.3L 2 door 4x4, ive noticed that when the weather is at least 50 degrees my truck will start surging at high way speeds around 60 mph. it didnt do it at all this winter, but.......as soon as the weather started warming up to around 50 degrees it started surging again, ive read all the posts for this but no clear answers, has anybody found what is causing this or have any ideas? thanks!!