2010 avalanche reduced engine power code p2135 replaced acc pedal didnt fix the problem

Question

the truck started going into reduced engine power for what seemed like no reason... scanner gave a code p2135. I let it go a few weeks because if you shut the truck down and restarted it again, the ck eng light was on but it ran fine. Then the light would go out after several cycles of the key but its still happening so I replaced the acc pedal position switch. I started the truck and while it was just at idle in the driveway it went into reduced power again so the pedal switch didnt fix the issue. Where do we go from here? This is my 3rd avalanche but the first to have any issues. Need to fix it before I get the last one 2013 is suposed to be the last year for them. Another good truck bites the dust.