I work on them and they're all pieces of sheet. Some guys have no problems while others can't seem to stay out of the dealer. The EGR game has really hurt these motors and right now, As has the newer fuels. The duramax seems to be in the lead in fighting this problem although it's not a landslide by any means.
The new Dodge diesel has had countless TSB's and can't seem to get to an oil change before it kicks a check engine light for EGR problems. Dodges answer in the TSB is to tell the customer they're not driving the truck hard enough...whatever! Not to mention numerous body, cab issues, and finally a new trans (Aisin-Warner) however this unit has been in the UD's, Mitsu's, Isuzu's, etc. for a few years now and can't hold a torque converter or low one way sprag to save it's life. And this is behind engine's with far less power and torque than the new Dodge engine puts out.
Ford is Ford. They traded a great motor and bad trans for a great trans (after recalls and updates in 04 and 05) and a bad motor. The 6.4 isn't any better in my opinion. Some of the 04's and 05's would make it from the dealership when brand new and crack the trans case across the street at the Fuel station when put into reverse. The fix for the 6.0 was to get rid of it for the 6.4. Nice!!
The Chevy is probably the best engine and trans package at this time however, GM has been plagued with electrical problems for the last 10 years plus. The Allison is the best overall trans out of the three and with some modifications can be a much better unit for heavy duty towing. Like Ford, The early 1000 series went through it's growing pains as well. And they like to crack the cases when guys off road or start adding the power. ABS issues, crap sensors made in Malaysia throughout the truck and the idiotic exposed front axles with independent suspension plague this truck.
All 3 are notorious brake eaters, wheel bearing, steering, ball-joint, suspension nightmares. These trucks are ALL GROCERY GETTERS!! Some guys get lucky, others not so. The guys that seem to run on the empty load side seem to do better than the guys who are hauling and towing heavy loads.
My opinion is a $50,000 should go 100,000 miles before major repairs. This used to be the threshold that the big three used to aim for. Now they are 50,000 mile throw away trucks. Sorry to any that are offended but this is what I see every day and hear from my customers.
I will say that the quality of diesel fuel is not doing these motors any favors as the newer fuel seems to have a bullseye on the fuel systems and we all know that diesels live on 2 things...quality fuel and low EGT's!!!
If you want to buy one, take your pick of which one you like the best and buy an extended warranty. You're gonna need it!!!