There is really no such thing as a "tune up" for a SHO. Is your car an ATX? If so, you are scheduled to replace the timing and accessory belts at 100K. If it is an MTX, the belts should have been replaced at 60K and shame on you. For either engine, the valve gaps and spark plugs are to be worked on a 60,000 mile schedule. There are several other parts that can be replaced during these services, but they are not part of the 60/100K maintenance schedules.
The engine gets "tighter" with the valve gapping because the gaps are usually reduced resulting in less impact noise from the cams on the shims. With the timing belt change, the valve timing is returned to its factory specs since the old timing belt has stretched minutely from its original length. During a proper reassembly, all the bolts are torqued down to their required specs. And, to top it off, it may also be the same effect that causes a car to drive better right after it has been washed.
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Scott
1991, 254K miles, glass hood, police grill, SVO shifter, Catz fogs,
K&N, 73mm MAF, Superchip, PP Y-pipe, Borla cat-back, 190 lph pump
Eibach/Tokico/polyurethane, SHO Shop front & rear strut braces,
16x7.5" Moda R1, 225/55ZR16 Bridgestone RE730, -1 deg camber x 4,
6 disc CD, Class II hitch, Silver award at SHOklahoma Car Show
