Got a 2003 Sonic with 496HO. Took it out for the first time this year and it would not go above 3000 rpm. Thought it was fuel related because it was surging so changed the inline filter bypassed the fuel switch and still surged. Replaced the fuel pump on the port side and it will go to about 3500rmp than breaks down. Anyone had this problem? Please HELP!!

Possibly in guardian mode? I'm not sure about the surging though. You need somebody to check the ecm for codes. Sill question, but is the drive resevoir full? One of my motors was limited to 3K due to low level in the resevoir, but I also had an alarm. Does the buzzer go off key on, engine off?

could be in a guardian mode. check the screen right at the fuel inlet before the filter. had a similar problem with a 496 one time

Keep in mind some of these engines are coming up with Bad spark plugs, That some still look good and others don't look so good out of the blue on you and make it run like this.

Mine also acted like that but was traced and solved by replacing fuel pumps.