Cummins are a quality engine but ive seen to many problems with the dodge surrounding them. The newer ones have electrical issues.
The old 6.5 GMs aren't big power houses but they do the job for the most part. They do have some problems with cracking the blocks in the cylinder walls and on the main bearing griddle. But a very reliable engine none the less, its used it alot to marine applications.
Duramax's 01-04 had problems with the injectors and injector harness. Causing the injectors to stick open. The rest of the years have had very little problems and the newest ones have the most power with 390hp and 780 ftlbs.
The 7.3's are a built proof engine, but the pre super-duty (86'-98) ones have a tendency to blow head gaskets.
Now the 6.0s. They have their issues (Head gaskets, FICM's, high pressure oil pumps, egr coolers, turbos, wiring harness) But these engines are built to such precision that when people don't maintain them they break down. Alot of people don't know that 6.0l dont use 15w40 for oil (It causes hard starts when cold) They use a heavy duty 10w30 or 5w40. 15w40 is only used for very heavy towing. Head gaskets were the main one and that was a design flaw, not enough head bolts. put in some studs done, although you have to pull the cab. FICM's Get it re-flashed or replaced. High pressure oil pumps fail because of dirty oil. The pumps gears are made out of composite materials and will break down in dirty oil and break apart, thus the truck stops running and shrapnel flows into your injectors possibly clogging them up. Egr coolers... simple a delete kit. Turbos stop working due to carbon build up the veins which seize them up and builds no boost. The reason is because no one uses a diesel like a diesel anymore, they use them as grocery getters and never run them up to clean out the carbon. That and High sulfur diesel was a culprit. The wiring harnesses rub in some places causing it to short out and cause a hard start. But these engine do not deserve this, if ford didn't rush the 6.0 to the market it could have been one of the best diesels out there. Theres guys making 700hp on stock rods, reliable! the 2006-2007 models have most of the problems worked out and can be found cheap.
6.4s I like them they can make big power. 1038hp on stock rods.
And the newest ford the 6.7. well only time will tell.
Trannies. Dodge autos junk untill the new ones
GM, 4l60e behind the 6.5s do the job. Allisions are amazing.
Ford, Torqshifts Ive never heard anything bad and the new ones behind the 6.7s are supposed to be better than the allisions. But im no tranny tech Its just what ive seen if you want reliability get a manual.