The P0773 code is an electrical fault code with the solenoid, not a mechanical one so I doubt that any trans fluid treatments will rectify the problem, although doing that service for your trans is probably not a bad idea anyway.
Below is some info cut and pasted from another thread that may help you get the problem fixed.
"FSM shows two possible codes for lockup solenoid. P0770 is for mechanical operation failure and P0773 is for electrical failure, although if the shift solenoid coil is bad you will need to replace solenoid. Order of inspection is 1. ECM terminal 2. ECM terminal harness to solenoid connector harness. 3. Check coil resistance of solenoid. 11-15 ohm. Could be just simple harness/wire connection problem. Pan will have to be removed for access to solenoid connector or solenoid. No expert, just looking at the manual. Maybe 1-2 hours labor??"
"just reset the code
it's a code that comes up for some people. it can be caused by something as simple as not fulling popping the shifter into the correct gear, or the tranny misshifting by accident.
if the code comes back, then dig deeper. chances are that it won't come back."
There was also a helpful link to diagnose this problem here:
http://autorepair.about.com/library/faqs/bl079i.htm
Linear Mode
