We were in a similar situation just a couple months ago (my daughter will be 4 next month & we just couldn't get over the hurdle to 100% trained). We went to a potty training seminar - they convinced me to go cold turkey on all pull-ups & night-time pants. We layered the bed - padding, then sheet, then more padding, then sheet, then more padding, then sheet - so that if there's an accident - you can just pull up 1 layer & go back to bed. Be prepared for a lot of laundry for a week or two.
We also gave 1 m&M for trying & 4 for poop in the potty. We made poop a big celebration - we called relatives & did a dance.
We also filled a bag with prizes (Jackie called them "poop surprises") - little things like tights, a small toy, whatever she asked for in the store, I would say yes, but you have to earn it out of the Poop prize bag.
Finally, we bought the book "Everyone poops" and read it a lot.
It was a lot, but we finally got over the hump -
good luck!
Mony