I'm always good at being an bad influencer. If funny as I continue to adjust my plans from other ideas I see on rigs, my wife keeps saying "What changed, I thought you already had the figured out" ... she doesn't get it
For the rear I'm running the spring under Deaver leaf pack that came with the Duff kit. I'm going to assume it's a 4" pack because after I installed it sat too low. When I called Duff, they realized they forgot to send me the extended shackles. The shackles they sent are 7.5" from center to center of the bolts, so approx 3" over stock which would net 1.5" of lift. I'm not a huge fan of the extended shackles because they're likely to get hit if I drop off a ledge, but they are about the best solution for my setup.
I'm running the drop pitman that came with the Duff kit. I'm pretty sure it's equivalent to the FA400 Skyjacker arm. As installed, it's not enough drop to get the drag link/ tie rod level. When I did the knuckle swap with the flipped TRE's, that got my rod ends up another 1"+ and leveled everything out. If I didn't do the knuckle swap I would have gotten the FA600 pitman arm.
Tire clearance in my opinion is perfect. The tires net out real close to a true 33". The wheels are 15x8 with 3.75" backspace. If the wheel is turned at exactly the right angle with one of the front corners stuffed I can just barely kiss the back corner of the fender. With stock wheels at 4.5" backspace, I rubbed my radius arms and shocks hard at full lock. After getting if flexed out this weekend and stuffing all 4 corners, 35's would have required quite a bit of fender cutting to make work.
Regarding stepping up to 5.5" from your 3" lift, I'm not sure your drop brackets will get you low enough to adjust all the camber out with adjusters. F150 coil spacers might be just enough to keep you from having to buy new drop brackets. Or it could be your opportunity to do cut and turned beams ... I'm pretty sure with correct length bump stops you can run 33's with 4.5-5" lift.
Thanks for following along with my build! Let me know if you have any other questions.