Looking at down grading trucks from 3500 to 2500 duramax. I bought the 3500 expecting I would do longer road trips but never did. The 3500 is a horrible ride and not so friendly for a daily. I bought another car to drive but the 2 payments are killing me, plus we are looking at build a house soon so I want to drop one of the payments. I know a 2500 will to the 38ZX fine I'm just wondering if it will tow a 43ZR or 42 Lighting.

Thoughts?

I tow mine with a 2500 Ford, does fine after I added airbags. I also have disc on all 3 axles.

It will work but I would suggest trailer be EOH and air bags and springs on the truck. FYI: My insurance made me submit my tow vehicle and rating info, then they wrote my policy with that info in it. Protecting them and me. So that negates the "I'll just add parts to my 250 to make it a 350" idea. Insurance told me truck must be factory rated to pull the weight. Check your insurance requirements on the bigger boat, sounds like your going to make a move?

Thought you were all about the big cabin boats!?

Yes

A new 2500 diesel with upgraded HD tires fully inflated while towing and maybe some air bags.

PLUS even more important a new trailer that's overbuilt and properly built! The majority of boat trailers a PURE garbage.

EOH disc on all 3 axles
F or G Load range 12-14ply tires fully inflated
HD wheels
Properly balanced load
Etc.

Same here.

I tow with a 2500 Duramax that's also my daily driver. Great truck, but is only rated to pull 13,000lbs on the hitch. I would think a 43ZR would be cutting it close, especially on a steel trailer. My Kevlar 39 Velocity on a aluminum trailer with only 1/4 tanks is 11,300lbs.

There are some things you can do to give it a better ride. I run Airlift 5000 bags with an on board compressor, Sulastic shackles, and Bilstein 5100 shocks.

You are talking about 2 different sized boats. The 42 Fountain is going to be smaller and lighter than the 43 Donzi. Keep that in mind. As such, a well equipped 3/4 ton can probably handle the Fountain.

However, if you are jumping up to the 43 Donzi, I think you are going to want the bigger truck and the extra tires in the rear to help you control the load.

You can get any of the Ram, GM, or Ford 1 tons in SRW now. On the Ford, the only thing different between them in 2017 SRW models is an extra leaf spring per my visual inspections at lots. I am not sure about the GMs. But with the Rams, their 2500 is a 4-corner coil spring suspension, and the 3500 is leafs in the back; BIG difference in capability, regardless of what capacities day.

The thing that is going to be most important is length. You want the crew cab/long bed setup. That's what is going to keep leverage over the load.
However, with the 43 Donzi, I think you will be much better off with DRW, regardless of what the capacities state.

I was but now I'm more about running in bigger water. The 38 is a great boat but there's been a few times The ride has been rough. Figure if I can extend the bow I can get by running in sloppier water. And all I do is sleep in the cabin.

Specs on the 43 ZR 15,030lbs Wet & 8'10" Beam VS 42 Lightning 13,450 Wet & 8'6" Beam. Add the trailers and gear
weight they both start getting heavy. The cabin height on the ZRs is tighter than the Lightning if that matters to you.

Sometimes there is not much difference in hitch tow ratings between a 2500 and 3500 rating truck. The big jump is when you switch from "conventional tow" to a fifth wheel/goosneck type trailer. That is when you see the 30,000 pound tow ratings the manufacturers claim. There are tow ratings on everybody's websites that show the cab, trailer, engine, gear ratio, etc.. combinations and what the tow ratings are.