I have a '99 4.6 with the automatic and when shifted into OD and especially upon lockup and under load it shudders and shakes the car rather roughly. I have searched and done a google search and found it to be a common problem but not with anyone here. I posted under the 4.6 forum but the trouble goes back to the early 90's according to google. I am hoping a few guys have had this and can reply as to what they had done to correct it. I know the converter will need replacing and am also looking for one that has more stall but still locks, is there one? Has anyone else had this problem? I have changed the fluid and filter and it got no better. I will call the shop tomorrow for an appointment but if anyone can share their experience I would appreciate it. Thanks, mark