Sometimes I can tell when my current DM fudges a roll to miss an attack or reduce damage. He has a tell in the specific way he pauses and breathes before announcing the roll, then tries to hurry to the next turn, which only seems to happen when someone is in a life-or-death scenario, but “luckily” survives.
Should I let him know he has a tell? Will it be less fun (or more stressful) for him if he knows I know?
Sure, and you can even improv a reason why that might be the case. “Normally he has a +9 to hit but he was distracted by how the barbarian just decapitated his minion in a single strike on a nat 20”