Towing - Not downshifting soon enough

[hoaxci5]

I tow an open trailer with my Jeep on it to go play at the offroad park. I have a 2001 Yukon XL, the trans has a new valve body from gmtransmissionparts and new(ish) fluid. It shifts fine when not towing, but activating the tow/haul mode it just about refuses to downshift when pull up a hill. Often I end up manually downshifting it to not lose my momentum, does anyone have an insight to what the problem could be?

 

[Rivieraracing]

Seriously, you need a tune for your truck! I did Blackbear years ago and still is one of the best upgrades I've done for my truck! Did get more power but mainly the shifting was dramatically better, like how it should have came from the dealership!
I especially noticed a vast improvement when towing as at the time I had a heavy toyhauler and it helped a ton pulling that anchor around without having to constantly shift up and down to get it to do what I wanted!