Serpentine belt problem

[1989GMCSIERRA]

I assume so. I took the old belt with me and matched it up by length and part number.

ok. I was asking because sometimes if the belt is longer it will slip. And in some cases they measure the belt with this tool abd they don’t allow for the old belt stretching.
The new belt may be putting pressure on one of the accessory pulleys where the old belt may be stretched enough that it doesn’t.

pop the belt off and spin all your pulleys by hand. Shake avd try to see if any have play in them. Could be a waterpump,they usually are the ones who tend to make noise