I've had the chicken three times and each time it was exactly the same.  The person I went with the first time also went later that week and said the chicken was exactly as we had it.  It might have been bad luck on your part.  

Also, Earl was there the first time I went and I asked if there were Sichuan peppercorns used in the coating for the chicken, even though that would be non-traditional, because I thought I tasted a numbing, and he said no peppercorns. He said that they use crushed coriander seed.  So I think it's that rather than the peppercorns you mention on the outside.

Only time I've had Thai fried chicken in the US that matched my favorites in Thailand.

The chicken and curry are stars and the best deal is the set meal that includes them both with roti.  The specials are more inconsistent, but try the "ground pork" which is very good, though Nakhon's version (kua kling) might be better.