vehicle shudder

at speeds of 35+, the vehicle vibrates violently on occasion until i back off the gas, but runs good when it's cold. Would taking it in to an engine diagnostic place help? i have run out of ideas. can they diagnose the transmission? Will the transmission give trouble codes as well as the engine?

Sounds like your torque converter is causing the shuddering. I'd recommend having a shop connect a scanner to the computer because the problem is most likely the torque converter (electronic) solenoid or regulator. A shop can see the voltage and plot it while driving the car. I have a 97 Bonneville that surges between 1700 and 2500 rpms. A electronic technician was able trace it to the torque converter solenoid and regulator, and the trans control valve assembly. By the way the solenoid requires dropping the trans and disassembling the trans.

fixed it by unplugging the converter------worked --go figure