OD light started to flash when I go into over drive.

My transmission went out. I took it to a shop and they rebuilt it. They replaced the clutches, planetary /forward gears, seals, torque converter, OD solenoid, and they rebuilt the valve body.
After I picked the truck OD light started to flash when I go into over drive.
The OD light starts to flash from around 44-70 MPH.
The code resets itself each time I start up the truck.
Anyway I took it back to shop and they replaced the OD solenoid twice. They replaced the valve and checked the valve body. Now they are going to take the torque converter out and test it.
The code is P0741. O/D solenoid stuck
The shop told me that their going to tear the trans and check it again because they told me it could be a small seal causing this problem.
The truck is wasting gas more than the average amount.
My question is if any one has worked with this particular trans and has experienced this same type of problem.
I have searched online and it seems like a common problem but no direct answer.
What can be causing this OD solenoid to stay stuck? What other possibilities besides the common components can cause this problem?
Electrical? Re flashing? A small seal?
Note: The O/D light never came on before I took it to the shop until it went out on the highway in overdrive.
-The OD switch on the column works and I can feel it switch in and out each time I command it.
-The truck also never wasted too much gas before I got the trans rebuilt.
-As from 12/2/10 the truck is still at the shop. They have replaced the OD solenoid again, replaced the valve and checked the valve body. They also took out on the highway with the scanner and the same code came on. Now they are going to send the torque converter out to be tested and than they are going tear the trans apart.