Still same transmission problem

[Linkspider]

99 Lincoln Continental

Transmision light comes on after about 40 miles of freeway driving, then when I slow down car starts shuddering like it is over heating in the transmission.

If I stop car for 30 mins or so to cool it down I can drive another 40 odd miles again.

I have done the transmission lube thing with 20oz of lubegard that just prelongs it and gives me a few extra miles before transmission light comes on.

I have replaced the torque convertor at great expense all ready made no difference one garage states change the whole transmission (for an arm and a leg) another states it could be faulty switches that are getting hot and sticking change those (for just my arm).

Has anyone been through this and solved the problem?