This is not meant to come across as rude but it is definitely user error somewhere in your process.
More than likely you are not waiting long enough on the charcoal. Do the lighter fluid method and apply lighter fluid very liberally. Light immediately after you have put it on the charcoal. 20 minutes really should be enough time and most of the coals should be white. Your basket of charcoal should be completely full to the top too.
Your 5lb chicken should have taken 1/2 the amount of time (generally speaking) you are stating. Try using the grate, no rebars in, lid closed, and slightly open the vent to 1/3 of the way open.
Try again and take pictures along the way. Take a picture of the basket of charcoal, what the charcoal looks like after 20 minutes, what the vent looks like, this will help the posters on here identify any issues they are seeing in your cook.