Mitsubishi: 97 Mitsubishi diamante transmission - reverse slips, mitsubishi diamante, transmission flush

Question
I have a 97 Diamante 3.5 w/ automatic transmission. The Reverse works when cold but slips when hot. ODBII error code P0750 "shift solenoid A malfunction". Also it could be the harness. My question: what is more probable, the solenoid or the harness?  

Answer
Most likely on that transmission there is a shift solenoid that went bad or it could be in the valve body... When is the last time that you did a transmission flush.. What fluid is in there. Mitsubishi require the Diamond ATF any other may throw that code also, be cause there is not the lubricates that is needed to shift Correctly