transmission, differentials, gearing, brake size, cooling ability, etc... all play a roll. Without knowing the differences in the Durango and Explorer in those areas its hard to know. I'm GUESSING the ecoboost is harder to keep cool vs. the Hemi with the turbo's adding to the heat load.
The 10R60 has a rating of 600nm or about 440 ft. lbs. of torque.
The 8HP70 has a rating of 700nm or about 516 ft. lbs. of torque.
The AWD system in both could also be limiting unless you are looking at the R/T rear wheel drive. The PTU(transfer case) in the Explorer uses a clutch setup to regulate power transmission. Im not sure what the limit on that is, but im sure somebody on here has exceeded it LOL.