I did the heater core on a 99 S-10 a few years ago. It ranks pretty high on the pain in the ass list. Lots of vacuum hoses to disconnect and keep track of, lots of screws in places no screws should ever be. During the 8 hours I did this, I made up a few new curse words and threw a few tools across the garage. It's one of the many reasons I would never even consider buying another GM product.
01 DRZ400S 93 GSXR750 13 Z1000