2003 Impala w/3.4 V6. has >332,000 right now. I had to put a new tranny in it at 150K, and new intake gaskets, and replace the camshaft and lifters at 285,000 It runs great, but it has something going wrong in the driveline. It slips and clunks when turning hard left. The AC is in need of a new line with the filter tube orifice in it.
I forgot to say it has the original bottom end and heads. I did have to put the thread inserts in the aluminum heads to improve the stock valve spring/rocker arm retention bolts.
I used Mobil 1 15,000 mile oil and that's how many highway miles I drove before I changed it. (I did have to replace the cam and lifters at 285K)