Not sure if this will help or not but I had a tbi 350 in my Astro van a few years ago and for the life of me I couldn't get it to stop squealing. Replaced pulleys, belt (x2), tensioner, nothing seemed to make it go away. Eventually, someone in a forum mentioned that they had solved the same issue with a Gatorback serp belt. Desperate, I tried it and it worked. I have no idea why, but might be worth a try.