help! my 2005 Duramax has been running fine with no issues. i put 260 miles on yesterday pulling my little car trailer to get insulation for my new shop. went to start it this morning to go to work and it idles about 500 RPM, knocks and shakes and has no throttle response with the MIL lit. All seems to be normal according to the gages. have had no issuse until now, about 165,000 miles. I don't have a way to read diagnostic codes. Any help would be greatly appreciated. I dont have any mods on the engine either.