I've tried everything I can possibly think of! I've even taken some seating charts from here but they seem to have different characters than I do. Argh! I just don't want to do anymore. This is soooo frustrating!

Still don't know why they keep posting things for me twice.

try leaving the slower eaters in line as long as possible for these last levels, if you have to seat them, don't seat them next to customers that annoy them, and use the chilli as much as possible for the slower eaters.  Try matching the colours only where you can.  If you get a pair come in and they do not match your colours exactly don't worry, just seat them with the highest colour.  For example if you get a pair who are purple and  red, and your seating only has purlple and yellow next to each other, if purple is x4 and yellow is x2, match the purple customer and don't worry about changing the colour of the seat.  You get enough customers on these levels to match up colours again.  Also use the jukebox as much as you can to keep the customers patient. 
 
One last thing, if you have got a row of cutomers waiting to leave and you are still waiting for a slow eater to finish so you can chain.  Forget about waiting for the slow eater and chain the other customers first so you can seat some more around the slower eater.
 
I hope this helps a little