Towing Capacity

I'd check to see if this is possible on the 3rd gens before relying on it. On my 2nd gen with a Tekonsha P3 through the factory harness, if I manually apply the trailer brake it also cuts the throttle. It's not immediate, but it definitely cuts it. I have never had to hit the lever "in the wild" but I was a bit surprised when I was dialing it in driving around the neighborhood trying to hold the truck at a steady speed while flipping the lever to see if the trailer wheels locked up.

 

It sounds like you only replaced one tire with a passenger tire and not both. Tires have to match, or your rebound won't match, and you get a fuckload of sway - especially on a trailer axle that doesn't have any dampening (shocks). Trailer tires flex a LOT more than truck tires, so you're effectively running a MUCH softer spring rate on the trailer tire side, leading to some crazy sway.

You definitely can't run passenger or LT tires on a tandem axle trailer because they NEED to flex when you're doing a tight turn. But on a single axle, you really get all the advantages with no disadvantages.

I replaced the tires on my camper with passenger ones and it's a night and day improvement. We just got back from a 1200 mile round trip, and have had 5 or 6 trips of a similar length so far on these tires and they look new, ride great. More info here: https://www.tacomaworld.com/threads/hammerhead-the-4x4-dclb-tow-and-trail-rig.671016/#post-23557724

30" tire vs crappy stock tires (had to run spacer/adapter to the 6 lug):