M.W.
Our 5 1/2 has the same issues - she too has been daytime trained for a long time...since she was just over 2. Our pediatrician (who we love) said some children can be upwards of 8 before their body signals them at night and/or has a large enough bladder to handle those hours (no matter how little they have at bedtime) - not what I wanted to hear, and probably not what you wanted to hear either. We don't talk much about it at all and we do not put on her goodnights underpants (larger version of pull ups) in front of anyone. We did have one talk about how to keep anyone from making comments about it that we do this in the bathroom in private and to not say anything at school (she's in kindergarten).
The hard thing in our house is her younger sister (our 4 year old daughter) can make it all night...our ped also said that it can be hereditary (my husband was almost 8)....so I'm not sure what to suggest...other than you are not alone and my understanding is it is biological.
Good Luck!