I'm with EZ. The keyword in your question is "dependable". They are ALL dependable, which is why we like them so much. What affects dependability is mostly the owner. If you have an original truck, like 1 of my 3 are, and you've maintained it, it's 100% dependable. That dependability dropped to 99% for a short time on the Moose Truck, when I ignored the warning signs that my tank selector valve was going out. First time it let me sit. The 7.3 ZF combo has the cavitation and DMF problems. Both of which can be dealt with with preventative care. The only thing you can do to prevent a DMF problem, is to replace it at some service interval. 6.9's are likely to need a set of headgaskets at some point. If you preventatively replace them when they get to leaking, then you won't have any surprises. Oil changes and quality parts are the two necessities. Folks who don't atone with the full measure of diligence will have undependable trucks, and I don't care what brand they drive. So what your really asking for I think, is what YEAR of IDI is the least susceptible to problems. My vote would be for a 1987 6.9 with a C6 automatic. No clutch issues, no glow plug issues, no cooling issues, no trans issues, no cavitation. Just an ugly truck that keeps on running, screaming it's head off with high RPM's.