Ive had an issue with my 03 Gt since I bought it, if youre on the throttle hard it squeals the belt until it shifts. Ive changed every pulley, the tensioner and have been through 3 belts and still havent been able to fix. Has anyone else had this issue or at least know of a way to fix it?
When there's a chronic problem with belt squeals that seems unsolvable the usual cause is one or more pulleys are out of alignment in the front to rear plane. Often the cause is a out of round crank damper. Typically this is from the rubber between the inner and outer ring drying out allowing the outer ring to slip or shift.
Take a look at the outer ring of the crank damper while the motor is running. Looking at the edge where the belt is use a fixed pointing device such as a screw driver lightly touch the edge of the outer crank damper ring. By touching the outer ring with the pointing device what you are looking for is to see if the gap between the pointing device and the crank damper ring to change as the motor rotates.
If the crank damper is out of round or out of square replacement is the only real option.