Any help appreciated. 1999 SLS, 105,000 miles. Car stalls sometimes when coming off hiway on exit ramp. Can go to neutral and start right back up. Recently noticed rough idle at stops. Dash display has two messages, service stability system and service idle air control. I have cleaned throttle body and iac with no help.

Codes stored:
C1286 Steering/lateral accelerometer sensor
C1287 Steering rate sensor malfunction

U1056 Loss of communication with rss
U1064 Loss of communication with dim

P0550 Power steering pressure switch
P1599 Engine stall
P1611 Loss of cvrtd serial data

I will be checking/cleaning battery terminals next. Never had a stall at stop just idle jumping a little. Should I replace the iac?, not sure this would cause a stall at high speeds. Had complete tune-up about a year ago, plugs, wires, fuel filter. Just replaced the air filter. Replaced power steering pressure hose 6 months ago. Only other thing noticed is a very high pitch sound from engine at idle.
Thanks