2005 Volvo S40 Question: Electrical issues, communication error.

Been on and off for a few months. Ill be driving and all of a sudden I get a brake failure stop safely light and all my gauges go dead. Sometimes from there the MPH will come back on and only the ABS service light stays. Turn the car off turn it back on and it says check engine, engine system service urgent turn it off take out the key and turn it back on and the urgent light is gone only the check engine light stays on until I turn if off and on again. Sometimes ill also get a power steering light as well. Also if I dont wait till the MPH comes back on and I turn off the car while the gages are dead ill get an immobilizer message for ten minutes then it starts up fine. Radio still works windows still work but sometimes driving is rough while its happening. So it definitely a High Speed Communication error. Already tested the alternator and changed the bad battery. I bought a new ecm but havent spent the money to take it to the dealer to get it re programmed cause I want to make sure that its the problem before doing so. Does anyone have any ideas on the issue? Its so frustrating and makes driving anywhere painful.