96 Windstar torque converter

My 96 Ford Windstar transmission was rebuilt some time ago and it has developed a surge/bucking feel in overdrive at about 1400-1600 rpm. I have tried to
isolate whether this problem was electrical or mechanical over the last few months. The #4 fuel injector has been changed along with a new set of plugwires and double platinum plugs. The engine has no noticeable miss at idle or acceleration, but as the transmission drops in to overdrive and rpm settles at around 1500,you get severe bucking until you change the engine rpm - problem disappears - then returns when idle drops back. I have tried driving in drive only(third) and although the rpm is higher, the problem still returns. Any ideas on whether this problem is electrical/sensor/computer/or transmission related? The trouble light is not on and a buddy of mine checked for any codes and said there were none showing up. One suggestion was warpped plates in the torque converter, any and all others appreciated.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

apply the brake just enough to send the brake signal to the ecu. This will tell the ecu to turn off the lock-up. If this cures it look for "trans doctor" additive. (I think its called, its in a small red tube). It has worked for me many times to stop the shudder. If it is the engine, clean MAF, replace fuel filter, plugs, wires.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.