Remove the 25 flat attack damage from Tryndamere's Q but make his fury go to 50% crit instead of 35%
So his damage is more predictable (takes fewer attacks to approach the average with 50% crit chance than it does 35%) and less spikey (less damage per crit) at early levels (especially levels 2 and 3 where he tends to cheese); specifically, it makes him more dependent on fury for damage and generally less annoying to play against early game.
It sounds weird that having more crit chance would be less annoying, but if you stop to think about it actually it does make sense-- basically it means you don't get surprised by an unlikely crit string of 2 or 3 crits that blows you to hell and back because of the bonus attack damage from Tryndamere's Q.
There really isn't anything surprising about being crit roughly every other attack, so 50% crit chance tends to be easier to play around than 35% because its more predictable-- and because each attack does less damage you aren't going to be blown up as hard by bad luck.
Having 85% crit chance at full build and no way to cap out without wasting some crit chance is kind of annoying to Tryndamere players anyway.
The tradeoff of 25 attack (pickaxe provides 25 ad and costs 875) for 15% crit chance (cloak provides 20% and costs 800) is actually probably a nerf, but I think he'd be fine with it mostly because he can access the crit chance at full fury sooner than he can access the 25 flat attack damage at level 9.