1991 Grand Marquis

not sure if i have a problem or not! shifting in od bout 45-50 mph seems to be little bit of jerking is this normal for mercury with overdrive?also this vehicle has 140,000 miles on it,runs smooth in just regular drive.

Mine is the same. If giving some gas, just before it might shift down from 4 to 3 it shudders. Has a little lurch from 3 to 4 also. I'm also at 140K, I'm not sure but I think some seal in the trans has weakened. For the 3-4 shift, I let off the gas for a sec, and for the 4-3, it's usually a hill or mountain or something, so I just manually go to 3rd until the top. (I know, what's the purpose of auto trans, etc etc...) Mine's the same, if left in 3rd it's always very smooth.