2003 Astro van, now needs new engine?

I have an astro 2003 with a vortec v 6, 4.3 L, running fine, took it in for an oil change and transmission fluid change and the repair shop blew the engine test driving it, saying I now need a new engine. Engine ran smooth as silk previously except for a slight hiccup when shifting, so we thought a fluid change would help. 129,000 miles. I'm suspicious the mechanic did the damage, since it's run reliably for 7 years. Regular oil changes, etc.