My 99 has about 240,xxx miles and I've never needed to put wires on it...At 180,xxx I put plugs in it and feel like I wasted my money, mileage stayed the same and truck runs identical...Other than stuff I broke being hard on it (rear locker, trans) and all the fluids all I have replaced is the AC compressor, AC tensioner and belt when that went bad, u-joints, fuel pump, and I had to flush the cooling system after about 225,xxx miles because it started getting hot pulling a load uphill in the summer...Oh and the oil pump in the transfer case wore through the case (kinda common, there is a metal tab that wears out and then the pump is rubbing on the case) I replaced the tab with GM's upgraded one and epoxied the hole closed.
Considering the hard life it has lived I'm still pretty happy with it.
Oh and if I was going to put shocks on it they would probably be Bilsteins, but they feel fine, no extra bounce, rides decent (extra springs on the back make the rear a bit stiff), handles well.