You know what...you can straight up kiss my......wait....
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Damn fanboys 
****Disclaimer: Everything I'm about to say is JUST my opinion.....****(I have to put this here or Shawn will set aside a solid week to fact-check everything I've said and compose War & Peace to refute everything
)
You're fooked at $13k looking for a cummins unless it's a Gen 1 2wd single cab, then you have the ricer crowd that's discovered their potential and snapping THOSE up for sleepers 
When it's all said and done, you'll likely pay more than you want for either. If you get a cummins, you will pay MORE for a good truck that's not got 1/2 mil miles on it. If you get a cherry low miles 6.0 that's not been studded you'll eventually pay for head gaskets and ARP studs, EGR delete...etc. It's been my experience that in the END you'll pay about the same, so it's just up to your personal preference.
I'll quote Matt from another thread:
THIS!!!! My best friend has been the lead mechanic at Cummins Atlantic in GSO for YEARS and has championed the cummins long enough for me to KNOW how good they are, but IMHO almost everything that surrounds that engine is just sub-par. Whether it's fit and finish, dash disintegrating, or tranny issues. Plus (again IMHO) the dodge has always been the ugly sister of the big 3. I had no issues with Chevy, other than the IFS and the fact that the chevy forums were littered with misinformation on which motor to avoid. Too many L's and B's and whatever...so I resolved to just stick to gas if I were going Chevy.
I had a $9k budget back in 2010. I knew what I wanted: Chevy, GAS crew cab, 4x4. Found one [USER=2412]@Toyota Dad[/USER] had on his lot. Even came with a snow plow!! It was PERFECT. Took the wife up to see it and she pulled the whole
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I'm not riding in THAT!!!!
Yeah it had paint fade issues, a tear in the drivers seat, but mechanically it was FINE. Still...NOPE! But...I got a boost in my budget 
For $18k you CAN slip into the diesel world...but you won't find a cummins with less than 150k, a chevy that hasn't been run harder than a Klinton assassin, or a Ford 7.3 (the previous holy grail)
In the end I found a 5 yr old 6.0, dually, crew cab, 4x4, that had 75k miles on it. It looked brand new. I couldn't pass on it.
I've had no regerts (but I knew what I was getting into)
Because the dodge tranny has a reputation worse than a 6.blow head gasket
Mine started drinking coolant....turned out the thermostat housing was cracked. Had EVERY sign of a blown head gasket....wouldn't leak until under a heavy load...then it would spray the car behind me. Housing fixed that.
Honestly....here is "the perfect truck"
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