holy shit, i LOVED our '96 impala, that car was awesome. i could still strangle my dad for selling it. hypertech, borla, cold air, you name it, and it was up for a cam and head work when he sold it.
i also love chevrolet/GMC engines because they're the least complicated to work with, if they cant resolve your issues in over two tries then they're incompetent, try another dealer with a mechanic thats worth a shit. however, chevrolet will not work on GMC and vice versa is true, though i dont know why
edited to add: i have a 2001 chevy 4x4 crew cab 8.1L, 72,000 miles. battery died (ac delco batteries are now notorious for leaking acid, if you have on i suggest replacing it NOW) and i had a crank position sensor go bad (FN computers) thats it. and damn that thing can run, 340hp factory stock.