I'm a new member to this forum, and in fact had been asking questions on this forum about "the big three" in 3/4 ton diesel trucks (thanks again folks!). Here's my view:
Comparing old and new technology is not fair for any truck: example a 2001 vs a 2013. Lots happens to technology and design. That said comparing trucks of the same year of manufacture is better. Here is what I found for 2013:
A disclaimer first: I used to be a die-hard GM fan and that's all I've owned for 25 years - cars and trucks. Then I got very "burned" with real lemon of a particular GM purchase just as the Great Recession hit and all that happened with GM after that.
When it came time to buy a truck I actually had a good look at all three as a result of my loyalty to GM in serious question. I'll be honest: I was very disappointed in GM. For the price, the look was OK, the diesel had my confidence, but the interior was a just not there at all - and that was the top end Denali!!
I then went to Ford. I REALLY liked them (they are not #1 in Canada and the US for nothing!). But.....that diesel engine had me really concerned. Ford has been through a few of them in the last 10 years or so. I know some will say the new one is great, but I'm sorry: only time (measured is years) will tell. If only Ford could get a quality time-tested diesel in their trucks....
Then we had a very hard look at Ram. The engine was a no-brainer being the Cummins (Case and later CaseIH had the foundation of that engine designed for agricultural use with Cummins in their joint effort, since 1984 - a great history!). But the Ram itself was the question. I was very shocked: outstanding interior, and with the 2013 they finally went to DEF. I was concerned about the stiff ride at first, but they have that "light load" option and it's great. I'm talking about the Long Horn.
Well guess what: I jumped to a Ram (2013) for the first time. The ride is great, the quality of the build is outstanding, the fuel mileage is very good, it's a beast when towing, and the interior is simply opulent.
I read recently that Ram is now #2 in trucks in Canada behind Ford (is it the same in the US?). That took a lot of work on Chrysler's part over the years and it's paid off. It's an impressive truck. Being a GM guy (and my Dad worked for a GM dealership for years) I was really disappointed with what I was getting for the money. But remember this: this is an opinion in looking for a 2013 model year, 3/4 ton diesel with as many bells and whistles as comes in a truck, as that's how I buy them. What a 2007 was or a 2016 might be for the "big three" will be different - and that's OK!