Trouble codes P0700 and P0740?

The P0700 isn't really a code, it is a flag that tells you that there is something setting another trouble code in the transmission control system. It is used to tell even a basic code reader that doesn't cover anything but engine related codes that there is a problem in another system. The P0740 is a real code though, it is indicating that there is a fault in the transmissions lock-up torque converter clutch control circuitry. Commonly it is an open circuit that sets this code, either a broken wire or the solenoid itself fails. The symptom you would see is that cruising down the road at a light throttle the converter locks up and the engine rpm drops by 100 or so rpm. Then with it locked up and you step on the throttle or brake the clutch unlocks and the rpms go back up just a small amount. It can also cause a decrease in fuel mileage but it would take you a long time to notice that. The solenoids are the most common failure, with the wiring connector being the next on the list. Checking the connection first is simple, Look at it closely for damage, it is in a spot where rodents like to chew. Damage of that sort is repaired, corrosion is also possible, for that my common approach on a high mileage vehicle in my area, is to simply cut the connector out of the circuit and connect the wires directly. The other option is to get a replacement connector and replace both sides. Test the solenoid resistance by measuring between the the solenoid connector and ground on each wire in the connector. Should be 14 to 25 ohms from each pin to ground. https://www.2carpros.com/articles/how-to-use-a-voltmeter
Lower or higher will trigger the code.
If the solenoid tests bad replacement isn't that difficult, you remove the three bolts that hold the solenoids to the transmission, disconnect the electrical connector and remove it, remove the filter under it and install the new parts. Plug in the connector and start the engine, shift it through each gear, then check for leaks around the replacement part. Go for a test drive and see if the converter clutch now operates properly.
The problem with those years is that the way it verifies the circuit is to turn on the solenoids and then it reads a drop in RPMs as proof the circuit works. That means that although the solenoids might be the issue, it could also be an issue inside the converter itself. The external parts would be the first place to look though.

This is the OE testing, Note step 7

2. Measure the transmission line pressure.
Is the line pressure within the service limit?
YES - Go to step 3.
NO - Repair the hydraulic system as necessary.

3. Replace the Lock-up Control Solenoid Assembly set.
4. Turn the ignition switch OFF, and reset the PCM memory by removing the BACK UP fuse in the passenger's under-dash fuse/relay box for more than 10 seconds.
5. Using the scan tool, check to be sure that the engine coolant temperature is 176°F (80°C) or above.
6. Drive the vehicle at 55 mph (88 km/h) for more than one minute.

7. Recheck for code P0740.
Does the OBD II scan tool indicate code P0740?
YES - Replace the transmission and torque converter.
NO - The system is OK at this time.

Replacement is simple, find the valves on top of the transmission as shown in the second image. They will look like the first image. Then you unplug the wire connector. Next remove the three bolts that hold them to the transmission. They then will come off. Under them is a filter, it also gets replaced. Then you put the new one in place and torque the bolts as shown in the third image. Then plug in the connector. Clear the codes and go for a drive, if the P0740 doesn't return you solved the problem.