I just installed a 2800 stall Performance Automatic torque converter in my '06 GT. It idles and drives great, but the problem is that the engine surges while coasting in gear. It will drop down to 500 RPM then back up to 750. Sometimes it will drop to 500 and jump all the way up to 1500. It seems like there is drag on the engine, which drags down the engine, which then compensates and boosts the RPM back up. On cold starts, sometimes it will die when dropped into gear. Any ideas?