Isuzu Amigo '99 Transmission Clunk

My 1999 Isuzu Amigo v6 2WD AT clunks between 2 and third gear on both upshift and downshift. This use to happen for about 2 days once a year and then go away. I regularly had the transmission flushed.



Recently, when jump starting the Amigo, the jumper cables fell and got wrapped around the fan drive shaft (yes, I’m an idiot, but just happy at this point to be uninjured). Now the clunking ALWAYS occurs, and the engine light is on.



I took the car in to get it checked, and the computer readout was a bunch of strange codes the mechanic didn’t recognize. He fully checkout out the transmission, and could find nothing wrong. His final diagnose: I need a new computer / ECM unit.



A new ecm is $1000, refurbed $500, so I am loathe to buy one and not have it work So I bought a used unit online ($125), but it didn’t change anything - still had the clunking. Now maybe this ECM had the same issue as my current one, but seems suspicious.



Any ideas? Thanks!