So I've searched and read tons of pages but don't seem to find feedback on towing. Specifically for those of you who've done Bilstein upgrade from stock and tow what was your before and after experience? Did you do lift and tires also in the same change?

After my first real trails in Moab I went down the rabbit hole of learning about lifts. On the way it seemed like upgrading suspension may solve my biggest issue with the 4runner. Here goes.

When towing a bit larger trailers it's not feeling like the truck is firmly in charge or the trailer is. Years past I've experienced serious sway. Sway may be a factor but isn't the only thing going on.

Loads:
17ft fishing boat, #3200 lbs single axle. No issues, trailers great
16ft fish house. #3800 lbs single axle. Just not confident and feel on edge. Hold speed to 55mph max. Afraid to run this on icy roads and that's kind of the whole point of owning one of these. For you from farther south just think of this as a camper
22ft glass boat, ~near #5000 lbs double axle and surge brakes. Same feeling as fish house but at this weight I understand. Only tow a couple times a year.

Options on the table:

1) Do nothing, it's not worth the money

2) 6112 + 5100 and stock height. Guessing this is the best answer but not the most fun

3) 6112 + 5100 and small lift. .8f/0r, 1.2f/1r, or 1.5f/1.5r. Using coils in the rear.

I have to replace an airbag on the rear so already be in there. My offroading consists of my first ever trip to Moab and Medano pass in CO. Regularly offroad in winter but typically snow on a frozen lake. Will be staying stock tire size for the foreseeable future. Don't have another car so this is a do everything. FYI - I'm fine with factory rake, don't care about leveling for just appearances sake.

Appreciate any help!

I only tow a tiny lightweight cargo trailer but I can address the top of the question if not the detail:

1. New rear springs--definitely.
2. Overall lift like 1.5/1 is great. You can choose various rates in the rear like Bilstein is stock rate, but you probably want more, so Eibach is 204 while Dobs has like 220lb options--and then beyond.

Now the tough part:
3. The best thing would be to get a rear shock with maximum adjustability such as the Dobs MRA with adjusters.

I personally was on the brink on going that route (6112 + Dobs MRA rear).

That way you can use a softer rear spring and stiffen the rear via the adjustments as needed.

Weight distribution hitch and airbags in the rear springs will provide more stability. trailer brake controller adjusted properly to weight will also help. 5k lbs glass bottom boat is the max towing capacity but with dual axle should be doable might take some trials to get it right.

I have airbags now and the fish house doesn't have brakes so a controller probably won't do me any good. This is the load I most care about. The big boat only gets towed spring and fall so less important.

Less familiar with weight distribution hitches. Looked at some pics now and don't think this will work. I see it attached to the trailer and hangs below the trailer frame. I need that space below the frame for clearance. Also at times I tow someone else's boat.

Not sure if I'm after the impossible here. Trying to help my daily driver out (95%) with my 5% towing.

I only have experience with towing a travel trailer hence my'advice.