The key to GEN I and II's is MAINTAINENCE before mods. The ever so popular "60k" service can be what saves your SHO from premature death. These 60,000 mile interval major services can be overlooked, and can cause unexpected problems that u don't want to deal with when on the road. These 60k services should be done, and done right. There's a few SHO's out there well over the 200k mark on stock motors and trannies because they have been serviced as the proper intervals. One SHO owner I know of has approx 270k on his 1991 that he bought brand new, has done all of the maintainence himself, and finally at 269k miles, had to replace his main rod bearings. Not bad for a 12-year-old, 269k mile V6 family sedan than pulls a boat in the summer time, has fun at the track, and gets used as a daily driver.
The 60k service includes the following major points:
Replace timing belt, waterpump, all gaskets, plug well seals, plugs/wires, valve lash adjustment (if necessary - usually on higher milage SHO's), front and rear main oil seals, crankshaft postion sensor.
There's a few other things but those are the major key items. The crank sensor should be replaced because it's mounted directly underneath the waterpump. The pump will usually leak over time (on average at least 80k miles) and will leak right on to the crank sensor, causing signal loss to the computer, which in turn tells the computer the crank is not turning, and shuts off fuel and spark - thus, NO GO. The crank sensor replacement requires tearing down the whole front side of the motor. So while everything is apart you have easy access to the timing belt and water pump, and also the front main seal, so that's why they are included in the 60k. Might as well do it while you're in there.
Other than this "minor" service and normal filter and fluid changes, the V6 SHO motor is one nice piece of motoring genious. Although it's hp and tq numbers don't seem so outstanding by today's standards, it will still allow you to put a whooping on most cars sporting even more than 60 hp more. It may only have a peak torque number or 200 (215 for the 3.2), but throughout the powerband that torque delivery is very flat and smooth. Unlike your average V8 pushrod motor that may have a peak tq number of 350, it will fall below at least to 200 or less than that very quickly. If you look at a dyno graph you will see that the SHO's torque stays well above the 180 mark from 2000-6500 rpm. This flat torque curve allows you take advantage of gearing, big time. Where else are you gonna find a 5-speed manual in a front drive car that can take 1st gear up to 40 mph, 2nd gear up to 65, 3rd up to 100 mph, etc. The SHO motor loves to be over 4000 rpm. It includes a unique dual intake runner system that opens up it's secondary intake ports at 3950 rpm. This dual intake runner system is what makes this flat torque curve possible. Do'nt mess with a SHO on the highway. You WILL be surprised.
As for the V8's:
The 60k interval has been moved to 100k miles. Doesn't involve the painstaking task of the wonderful crank sensor ordeal the V6 suffers from. The V8's are awesome motor's with excellent durability. The one thing that makes the V8 SHO look bad is the cam issue. It's a Ford defect and they deny it to this day. What happens is a cam can break free from the gear sprocket that drives it. This is bad. This probalem can be avoided by using spot welds on each cam to ensure the cam will never ever separate from the gear for the life of the car. It's bit pricey but there are SHO Guru's out there will do it for less, and in about 4-6 hours total.
The Automatic transaxle in any SHO is not the best in the world, I'll tell you that. 93's suffer from early death due to poor programming in the computer. 94-95 offered a different computer that made the shift points better and controlled pressure better. So many 93 guys often swap in the 94-95's D4U1 computer. 95's supposedly had undated internals, but I never saw it in my 95 ATX SHO. Had enough nightmares with that tranny. The GEN III's tranny seems to hold up better. Haven't heard of as many failures as I have heard of GEN II's. Gen II's can also be "re-enforced" woth the use of a Ted Beraux performance lifetime performance module (LPM for short - or basically, a Chip) that adjust the shift points making them firmer, quicker, and overall better than stock. You manually shift the Auto tranny with one of those, and you will chirp second gear, and engage the gear u want, when u want, immediately. No more slushbox slower-than-hell shifting. This increase in line pressure that the LPM allows will actually prolong the life of the tranny. Having the tranny shift mushy and slow is what kills them.
There's more info, but I'm tired. Enjoy!