Stockers are more than likely topping out.
5100s are good for 1.5- 2" rear lifts depending on who u talk to. I dont mean "this guy or that guy on a forum", i mean calling toytec, downsouth motorsports, wheelers offroad, sdhq, etc.
Even then, they limit the rear end. More droop can be had with the extended 5100s but the bumpstops need to be spaced.
Using blocks with weight on the back of the truck past 1" has been said to make the flattening of our already pisspoor leafpacks come on faster.
Its also stated blocks over 1" can increase axlewrap. This may or may not be a factor since the weight of the cap MIGHT help with weight and lessen the driveline angle.
Ymmv