Start with checking the battery under a load test and then check to see if the alternator is charging the battery. I would also install an extra negitive cable to the engine and frame.Ok, so I am finding problem after problem with my GTS, but alas I am not giving up on it. Right now, one of my main problems is the charging system. I bought a new battery when I first got the car back in December. It would stall every now and then but, when looking at the scanner, the voltage is jumping around everywhere. I swaps out the alternator with a remanu one from DB Electrical and I am still having the same problem. I ordered a new 4 wire plug because mine looks like it's seen better days. The only other thing it could be I am thinking is the ECM as it regulates voltage with the internal regulator. Has anyone had to repair/replace an ECM because of this problem? I am planning ahead here in case I have to have the ECM sent off for repair.