P0740 Code help

[Yamifz1]

In the last few days I have been getting a P0740 code "torque converter solenoid open" I can shut off the truck and reset the code using my Diablo but after a day or so it will come back. So this leads me to believe that it is a faulty switch but I'm not sure.
However today I was on the highway when the code came up and that's when I noticed that my RPM were higher than normal and it did not seem to switch into overdrive and at lower speeds or reduced throttle the "ECO" did not come on.I stopped, reset the code and everything seems to work fine now.
I put in a EDGE 3000 stall converter in it about 2 years ago, I can't see there being an issue with that... Hopefully not.
Any ideas on how to test or maybe determine where the fault is would be greatly appreciated. Don't want to have to go to a shop just before Christmas and spend a few grand getting it fixed if there is something I can do about it.

 

[Yamifz1]

so I noticed today that there was a couple of small oil stains in my driveway, hard to tell if it's transmission fluid but it may be as I believe I have had a very slow leak in my transmission cooling line for a while now (been meaning to fix it but it has been so little) It appears that things may have sped up a bit.
Is it possible to get this code because of a loss of fluid? I'm thinking yes because the torque converter works on pressure if i'm not wrong and a loss of fluid would reduce the pressure I think..... Any thoughts?

 

[Tach_tech]

Low fluid definitely could cause it, but if fluid level is good, I’d be betting on a failed torque converter.

 

[Rampant]

Here is some info from Alldata on that code:

P0740-TCC OUT OF RANGE

For a complete wiring diagram, refer to the Wiring Information .

Theory of Operation

When the transmission is in 2nd gear through 6th gear, the Torque Converter Clutch (TCC) can be engaged when certain conditions are met. The TCC piston is electronically modulated by increasing the duty cycle of the L/R-TCC Solenoid until the torque converter slip difference (difference between engine and transmission input speed) is within 60 rpm. Then the L/R-TCC solenoid is fully energized (FEMCC - 100% duty cycle). Torque converter slip is monitored in FEMCC to ensure adequate clutch capacity.

- When Monitored:
During Electronically Modulated Converter Clutch (EMCC) Operation.

- Set Condition:
Transmission must be in EMCC with input speed greater than 1750 rpm. The L/R-TCC Solenoid achieves the maximum duty cycle and can not pull engine speed within 60 rpm of input speed. Also when the transmission is in FEMCC and the engine slips TCC more than 100 rpm for 10 seconds then DTC P0740 will set. This DTC can take up to five minutes of problem identification before illuminating the MIL.

There is a bunch more info and diagnostic procedures concerning this code, but they require you to have a scan tool capable of monitoring torque converter slippage and detect commanded inputs... I am assuming if you had access to one, you wouldn't be asking on here.