Tranny Troubles?

[cstruc]

Last week I noticed some trouble with my car (93 Custom Sedan, 3.1L). Any speed below 40 mph (65/70 km/h) it is fine but above that speed the engine has a tendancy to shake pretty badly if the RPMs are between 1800 and 2500, it feels like it is missing, but I don't think that's the case (only happens above 40 and I replaced the plugs and wires in the spring).

If I'm on the highway and I try to set the cruise at 60 it's fine until the RPMs settle and drop down, at which point it starts shaking. If I press on the accelerator it doesn't accomplish much unless I put it down to the floor (then it kicks out of it) or I can ease of the gas and slowly start to accelerate to correct the problem.

It's got 177,000 miles on it so it wouldn't surprise me too much if it was the tranny, but anyone have any ideas?

[BNaylor]

When was the last transaxle service. ATF and screen filter?

It sounds like an issue with the torque converter clutch (TCC lock/unlock) but that can also be caused by a secondary ignition issue like plugs, wires, or coil packs.