Can you help?

[wegone]

My buddy is trying to find out how much he can tow with his truck.
It's a 2015 F-150 4x4 supercrew with the 3.5 motor.

He says its the eco boost, but I thought they came with a heavier GVWR than whats on the sticker?

He was pulling his 23 foot travel trailer at 6k and he said he had to take it out of tow/haul going down a slight grade as it rev'd the engine really high.
Its a 6 speed with the 3.53 tranny I think....

Any help I can pass on would help...thanks guys!