M.C.
#1 Throw out the pullups and switch to just undies and pants even at night.
#2 Take him to the potty every 1/2 hr whether he goes or not
#3 NEVER put a diaper on him again for any reason
#4 It will take patience and the first couple of days he will mess probably 6 or so times a day but it will get better every day and be prepared to do laundry and have at least 10 pairs of undies and pants to start.
I did this at 24 months with my son and he was down to 1 accident a day after 2 weeks and no night time messes and after 2 months there were no accidents.
Best of luck