This is the second time I had this misfire problem. When my car reaches around 40 mph it stumbles and shakes vigorously. When I'm under or above 40 mph it still shakes but not as hard. I'm saving the compression test for last but is there a certain coil or spark plug that causes a misfire at this speed? I have spare top and bottom coil packs but not the middle. I have brand new autolite wires and double platinum plugs just waiting to be used. Could this be an ICM problem?

All 3 coils are identical. It doesn't matter where you put them, as long as each respective post location still goes to the correct cylinder.

Check your 3 coils (and the two spares) using the procedure in Techinfo, and report the numbers back here for the primaries and secondaries of each coil (label them all so you know which one tested as what later).

We'll go from there.

EDIT: 92 SSE? L27? Have you converted to the 3-coil Delco system to replace the Magnavox, or did the car come with the Delco?

Actually, it already has the delco packs, but I've just recently found out my problem. While driving 75 mph on the I80/I294 going to Merrillville in Indiana. The tread on my rear left tire just came off. My car started swerving, I almost lost control while there was a semi truck on the side of me. Luckily, I made it to the side of the road and checked the tire (tread was gone along with my center cap). It was still inflated so I drove cautiously to my destination (which was important) since I was already far away from home. Come to find out the car drove like it had a new engine in it. It was kind of odd to me how the car shook and stumbled around 40 mph due to a bad tire. Thank God though, I was scared that it was bad compression (I always think for the worst). How long do you think this tire will last without tread? I guess I'll get a used tire to last me through the winter since I'm putting rims on for the spring. Oh and now I have to bother NHolds for a new center cap logo.

Probably about 10 seconds...

I know that you said you already drove on it once, but do not drive it again. It is extremly not safe.

In all honestly, you should park the car untill you get a replacement tire. I personally would not even drive it up to a tire shop, even if it was only a mile away. I would take the rim off and run it up to the shop to get a different tire installed.