If you were calling a former landlord on a prospective tenant would you want an accurate history or what?
No moral dilemma here , other than a concern as to why you would think there is a dilemma...
"They are really nice people but were consistently 2-3 months behind" is the truth, that's all you need to say, the facts. Some landlords may be ok with that, others not.
Your tenants behavior and choices are their responsibility, do not make it yours.