Okay. Would error codes show on my Vesselview? There are none.
Possibly, mercruiser has used smartcraft/vesselview for the better part of 20 years. It should at least indicate a fault but may or may not give detailed information depending on the model/style/age of the vesselview.
You have an ecm that is mapped/programmed for a stock 5.7/350 on a 6.3/383. It is going to run lean. The ecm is providing injector pluse width for less displacement. If there are no faults the ecm will not change the outputs and even if there were faults it'd compensate for a 5.7/350 not a 6.3/383. The ecm has no idea what engine is under it, only the information provided from the engine sensors regarding coolant temp, rpm, air temp/pressure/vacuum, oil pressure, etc..
If you're looking for performance you need a new ecm or have yours reflashed. I don't think mercury will reflash your ecm and am unsure of any aftermarket companies that reflash the 555. Mercury does/did sell a 383 stroker mpi so you maybe can buy an ecm from them
As far as running your setup as currently based it may be okay if you take it easy but if you want top performance you need to spend some money
