Hi all...I posted this in the Tech forum but I guess this is the place for Technicians...This truck will run fine for 30-45 minutes..Then it will start stumbling and then backfiring,but keeps running...If you shut it off during backfiring mode it wont start till after it sits awhile..I was told the 771 code was for a bad 02 sensor,I changed it but its still doing the same thing...The LP Reg and Mixer/Electric throttle body have been changed not long ago...Any help would be much appreciated...Thanks