My 2003 Chevy Silverado 4x4 has the 5.3 liter V-8 engine. I'm at 77,000 miles and haven't needed to do a tune up, although lately it is feeling a tad sluggish. I thought I would replace the spark plugs even thought the service manual says they don't need it until the 100,000 mark. So it got me thinking maybe I should just take it to a repair shop for a tune up. My dealer sucks so bad I won't even think of taking it there. Frankly I don't trust any of the other repair shops in town either - they have all tried to take advantage of me or my gal's car over time. So I usually go to them when I know exactly what I need done and have a feel for what it should cost. But with these modern computerized engines I'm not so sure what is needed for a tune up. Heck, I can replace the plugs, do my own oil changes, air filter, etc. but they always seem to charge high fees for "hooking it up to the computer" without being clear what was adjusted or recalibrated or whatever. That's where I feel like I am being had. I did have an oxygen sensor replaced a few months ago - I'm thinking the performance dropped a bit then but not sure. I'm probably just being paranoid but I'm sure my horrible dealer would have skipped any computer adjustments or recalibration steps if any where called for by replacing that thing.