As for the steering wheel shaking, 1st thing I'd have checked or done is have your wheels balanced. While your at it, don't just do them up front; have all 4 tires done. Before having an alignment done, a decent shop should check for any play for loose tie-rods, ball-joints. While the fiero is an older car (if budget pernits) changing 20 years bushing can make a difference. Also, have the front sway-bar bushings and end-links checked for wear, cracking, etc...
1st off if my steering wheel is shaking while I drive (not the loose torx bits shaking) is it safe to assume it is the tie rods?
What all do we have? Are they front, rear, upper, lower, inner, or outer? Which usually go bad?
I had the exact same thing in my Volkswagen Bus. When I would drive down the road, the steering wheel would be "ok" at really slow speeds, or when turning, but when I was trying to go in a straight line, the steering wheel would start to violently shake back and forth by about 15-20 degrees.
It turned out to be the tie rods. I replaced the inner and outter tie rods and it immediately solved the problem. However, in addition to that, you also have a failed steering damper. It's a shock absorber that's supposed to limit the amount of vibrational feedback to the steering wheel. I think the Fiero Store sells it for $59. The Fiero Store also sells the Tie Rods in a "package" for the front. They are having a sale on the 28th for 15% off. That's when I'm going to order a bunch of stuff.
The tie rods are the only thing on your Fiero that would cause this symptom. Because... basically... one (or both) of your wheels are violently flapping back and forth slightly (left to right) while you're trying to drive because there is so much play in the wheel.
If this happenend "suddenly" , and you just had tires replaced and balanced, I would check for loose lugnuts and missing wheel weights. Usually, if you have a worn component(s) in the suspension, and new tires are installed, the new tire will mask the suspension wear problem, rather than make it worse.
Check the lugnuts!
But, if you've got the $ and you're swapping in an L67, go for the rebuild on the suspension. Fiero Store has a "handling package" that includes Eibach springs, F & R sway bars and KYB shocks. Renew the balljoints, ends and links, install new bushings and you've pretty well got a new car! If you replace bushings, think hard about stock vs. urethane. Ogre likes stock bushings and poly sway bar hardware, I put poly everywhere. All poly increases harshness considerably.
If it just started when you had your Falkens replaced, maybe it might have something to do with the tires or tire balance? Tire guys are not always perfect, nobody ever is, and even their machines aren't perfect.
Unless you just like throwing money at the problem it might be worthwhile to rule out the tires first.