massive vibration on acceleration and when shifting into overdrive

[tonypuka]

I have a 1995 LeSabre, with automatic transmission.
When I get to about 45 and it shifts to overdrive, the motor shakes like there is a broken motor mount. I have to let off the accelerator and have it shift out of overdrive to get any acceleration back.
Engine runs rough most of the time now, not just in OD. I changed spark plugs this summer, not plug wires tho , and the transmission is a 1 year old rebuild. Often I also get a very high idle at start up. Not a smooth drive at this time.
I plan on cleaning my IAC for the idle issue, but I am stumped by this sudden,violent chugging,vibrating,shaking in overdrive.

[HotZ28]

This “vibration” is a usually related to secondary ignition misfire. i.e. coils, wires, plugs. If the wires are original, they could have been damaged when the plugs were changed. Start by replacing the wires with a high quality wire set such as ACDelco, Belden, MSD, or Autolite Pro-series. Never use the cheap wire sets on the DIS ignition! You could have a bad coil also, but change the wires first.

[Hapynzap]

I recently replaced my wire-set with the Autolite professional and they matched up great. The metal heat shields went on the plug boots just fine too. Part No.
97069 at Checker for $24.29