So I was looking at the armors the other day and decided to think of how I could get the highest possible DT in preparation for my showdown with the end boss. While doing this I thought about DT in general and thought about trying to calculate the highest possible DT one could attain in the game.

This is my theory crafting, feel free to add or adjust if you see any conflicts or mistakes

Toughness (2): 6
Sub-Dermal Implant: 4
Reinforced Spine: 2
Remnants Armor Helmet: 8
Remnants Power Armor: 28
Whiskey (with Cass)/ Upgraded ED-E: 2
Nuka Cola Quartz: 3
Datura Hide: 1

This gives a non-situational DT of 54

there are other DT perks that are situational and can further increase your DT

Stonewall: 5 DT vs melee
Nerd Rage: 15 DT when less than 20% hp
In shining armor: 5 DT vs energy weapons if in metal plate
Fight the power: 2 DT if fighting NCR, BoS, or Legion
hit the deck: 25 DT against explosives

so at less than 20% hp and being attacked by a legion/BoS/or NCR member with either a melee weapon or energy weapon you could get a DT of 72

at less than 20% hp and being attacked by a legion/BoS/NCR member with explosives you could get a DT of 92!

again, feel free to correct me if I am wrong