I bought my Gold 2001 ST used about 3-4 years ago with 127K. Don't know what the maintenace history was from the previous owners (2), but since I got it, I've done alot. First thing I did was a full tune-up (plug, wires, coil pack, fuel filter, K&N CAI cone filter), I've changed the differential fluid, drop tranny pan and changed filter, topped off with about 5-6 quarts of fresh tranny fluid. I routinely do my own oil changes, which I transitioned from Syn Blend to Full Synthetic with no issues. My exhausted broke off where it connects to the Cats, instead of having it welded, i insalled a new MagnaFlow Cat Back exhaust. And just recently, my alternator died out, which I replaced and bought a new battery, since old one was only holding about 50% charge.
Basically, as stated before, you take care of her and she'll take care of you. My wife always tells me I love my truck more than her because i'm always tinkering around and pampering her. Now at 153K and counting and throughout all the work I have done, she has always driven great. Depending on my driving style, I get between 15 to 19 mpg's and am average close to 17 mpg's combined.
MY goal is 300K plus.