Michele,
If you are considering a truck bigger than a 150/1500 (1/2 ton), I would strongly consider the diesel. It will be more expensive, but towing with a diesel is far nicer than a large gasser. Be warned. There is a saying, once you've gone diesel, you'll never go back.
I'm on my 3rd Ford Crewcab diesel, but the race team had 2 others. I've experienced the good, bad, and ugly of the Ford diesels since the old 7.3 Powerstrokes (up to 2002). You will have no problem getting 3 car seats across in the rear. The Ford crewcabs have some of the largest rear seat space. I get 3 large adults in mine with room to spare. The 2005 Ford diesel was the 6.0. The remaining ones should be pretty reliable. They made decent power for the time (570 lb/ft of torque)- [On a side note, diesels make power differently than a gas motor. Horsepower (HP) is what you hear in all the marketing, but torque is what you really want when towing. Think of it this way. Torque is what accelerates you. HP is what gives you maximum speed. Gas engines generally make the same amount of HP as torque. Diesels typically make twice as much torque than HP. Remember torque is what you want for towing.]
The newest Ford diesels (6.7) make 440 HP/ 925 lb ft (torque). That is best in class right now. The 6.0 in the 2005 made 325 HP/ 570 lb ft. That sounds like a huge difference, but if you aren't towing over 10,000 lbs, I don't think it would make that much difference. My 2002 7.3 diesel made 275 HP and 535 lb ft. It pulled my 7000 and 8500 lb campers with no problem and I got 11 mpg towing at 75-80. Can't do that with my 2011 making a lot more power.
The 6.0 was the last non-emission diesel too. That means no DPF (diesel particulate filter) and "regens" (process to clean the DPF by burning extra fuel. aka. worse fuel mileage) and no need for DEF (diesel emissions fluid) that gets injected into the exhaust to control emissions. I would strongly recommend staying away from the Ford 6.4 diesel (2008-2010- there's a reason they only made it for 3 years) I had a 2008. It was the first of the "emissions diesels". It made decent power and in the 30,000 miles I had it, I never had any issues, but it got HORRIBLE fuel mileage. 8.5 mpg towing the same camper that I would get 11 mpg towing faster in my 2002. I hear if you remove all the emissions stuff and "chip" them, you get great power, dependability AND good fuel mileage, but that makes them illegal in many states.
Now for the bad. The 6.0 had some serious injector issues. Many had to have the fuel injectors replaced by 75,000 miles. Quite a few in under 30,000 miles. Some trucks ended up having entire motors replaced. Our race team had a 2006 with the 6.0. It had 2 injectors go bad on the return trip from racing in Utah (from St Louis). One failed about 20 miles from the shop, the other died in the shop parking lot trying to figure out why the truck was running so bad. We replaced all 8. The general rule has been, if the truck has more than 80,000 miles on it, it either has had the injectors replaced (in which it should be fine) or they are fine and won't cause any problems.
If you aren't married to a specific brand, I would look at Dodge and GMC/Chevy too. I've always been a Ford truck person (raced Mustangs and was a Ford Racing sanctioned driver), but all 3 have their strong points. (Dodge- engines (but terrible interior and overall truck durability), GMC- transmissions- the Allison really is a nice transmission , Ford- best all around truck durability and interiors) [Not trying to incite a "truck war". Just my opinion based on driving and towing with all 3- your mileage may vary]
Have fun shopping!
j
