From the sidewall clearance side of things, it's gonna depend more on the rim/tire.
From the caster/alignment side of things, I'd say a full 3" is gonna put it on the fence; mine (OME heavies, no trim packers) is at about 2", and it's just at spec. when I first installed, and it was at 2.5", the right wheel was just out of spec for caster.

 

Yes, forgot to add that, generally concerned with alignment and ball joint issues.

 

The ball joints will be fine at 3". But if you go ahead and spring for the UCAs, you'll be able to get all the caster you can shake a stick at, and it'll ride a lot smoother/straighter on the interstate. My wheel is a little tender, I'd like more resistance... I've got the OEM UCAs, and need to get some Light Racing....

 

Thanks......appreciate the opinions.
Have had the TT since 2008, now out of warranty, so let the mods begin!

Starting off with a set of 5100s with stock springs and diff drop.
Upsizing slightly to 285/75/16

 

With the 5100's you don't need the diff drop. It is really not needed unless you go with more than 3" of lift.

 

^^^ Truth. The half-shafts start (at oem ride height) angled up toward the wheel... unlike the taco and runner suspension.... so when you lift ~2", it's almost the same angle, but down. so your over all CV flex doesn't change too awful much.
That being said, your 1.25" inner CV boot clamp is probably going to start seeping; there are threads around to upgrade it to a better clamp, but just keep an eye on it. your truck is young, it may not be an issue for many moons.

 

Wow,......enough material here to read to make your head spin.
Went ahead and ordered a LR UCA set........

Going to go 2.5 on the front with the Bilsteins and 1.5 on the rear with spacers, until I figure out the springs rates I need.