Belts scream for various reasons. Although new to you it may be old stock. The belt being too narrow.. it seams to be going rather deep in your crank pulley. Belt being too loose or too much load. Is your battery discharged so that your alternator is really working? Once a belt has slipped a lot and gets shiny, it will scream no matter what you do. Possibly a little wider belt would help. The numbering denotes the length and width of the belt. I usually tighten a belt until it deflects about 3/4" at the longest span and then recheck it after it has run for a while.