What should I stay away from?

If you go gas get the biggest engine option with the highest numerical gearing. In that vintage you will see mostly 4spd autos so the diff gear is more important.

Buying a used vehicle is iffy, especially after last year's "super-storm".

There are a large number of vehicles showing up in the Midwest with "washed" salvage titles.

For 250/2500/350/3500 diesels, I'd suggest avoiding the 2003 - 2007 Ford 6.0L Diesel.

Here's why

When you start shopping the used market, you will find they APPEAR to be a bargain. There's a reason they sell for less.

The 2008 - 2010 6.4L diesel Ford used was somewhat better, but I'm not a big fan of that one either, mostly due to it's propensity for self destruction earlier than it should.

There's really no major "avoid this" truck on my list when it comes to "half tons" 150/1500 series. They are all pretty reliable.

The gas engine 250/2500s from the big 3 are all good choices too IMO.

any sales person who says trust me!

just get any of the popular 1/2 tons. Unlikely you have the trailer right at 7700lbs. Ford, Dodge, GM, Toyota would should all handle 7000lbs.

Do you know your actual weights?

climbing to 8000lbs will require a 3/4ton which opens up a new can of worms.

Any truck COULD have issues. With a gasser even if you had a catastrophic failure it wouldn't cost more than a couple of grand to make it perfect again.

Find something you like you can afford and buy it. I wouldn't over think it.

They truly are all the same.