This may be a long shot but I had a similar problem a couple years ago in my Duster. I was at the local drag strip making my very first pass in the car. I shifted manually around 5,000rpm, right when I shifted into second the engine completely bogged down. I thought it was going to die before the finish line but didn't. Rpms were dropping and sputtering. I released the gas and everything was fine. I just coasted the rest of the way. After I talked with many people my guess was fuel starvation. Have you ever replaced the fuel tank or sending unit in your car? I still had my original parts in my Duster. We raplaced both the tank and sending unit. Fuel line was already new. I have never had that problem happen since. The sock on the sending unit gets clogged up. Mine was pretty tore up.
Just a thought, nice Dart by the way.
