Well regular can be both checked by mileage and by date.
From what I've read on the net and what I've been told by some transmission ppl some recommend 20k/km, 40k/km,50k/km.
Some recommend 6 months, 8 months, 1 year.
It's all due to your driving habits.
Long high speed driving.
Plenty stop n go traffic.
So that's where you decide what regular is and how it applies to you.
(My opinion)the addition of the oil cooler is the best option.