As I'm sure you are aware, the trim gauges need to be calibrated so that when trimming out after the boat comes on-plane and you set both motors at say, 4 bars, that they are actually equally trimmed. On the larger motors the sender reostat itself has slotted holes so it can be rotated to adjust the gauge reading. On the smaller motors like the 150s I had on a previous boat the reostats were fixed and you rotated a striker to adjust the gauge reading. It sounds like from your description that your motors may not be trimmed like you think. When the gauges are matched but motors are not. Have you checked?