Sounds like "heat checks" to me. Have it resurfaced, then see how bad they are. If the flywheel doesn't "clean up", by all means; replace it.
The flywheel shouldn't blow-up unless you like to rev up your engine and side-step the clutch at stop lights. GMC engine are relatively low speed engines, with stock redline about 4000-4500 rpm. I know I never ran mine that high; but it did see the 3k's........
Take it to at least two different shops before you throw it out; it's always good to get a second opinion.
