95 bonneville sse-shudder/vibration

My 95 bonneville sse has about 156k on it. It has been very well maintained for the three years I have owned it and has never given me problems. For the last two months, it has been making a "vibration" type noise/feel, almost like you are going over rumble strips . It usually only does it at about 40-45 and at about 70-75. It only does it when you are accelerating. I have had the plugs/wires replaced, the fuel filter, fuel pump checked. I took it to two tranny shops for road tests. The first one said for sure he thought it is the torue converter clutch, hence the "shudder" noise. The other one said he'd get a diagnosis done first before focusing on the tranny. Now when it does it lately-it acts sluggish in a way. I also had the cat. converter looked at; they said that wouldn't be their first guess. I guess my questions are.....has anyone had this prob with bonny's and it hasn't been setting any codes off either-should I still pay to have a diagnosis done? Would a diagnosis show a TCC problem? Please help if you can!!

i have the same problem w/ my 92 Bonn i have no idea what it is

I am getting a full computer diagnosis this weekend, so I will post what they say:)

cool cant wait

A full scan should show a TCC problem, my 95 shifts out of OD after about 30 minutes of driving. I think it's code 0401.

is that why it shudders?

I have no idea, but it is possible.