I've had a 3rd gen ram and now have a 4th gen. Here are the problems that are very common on the 4th gen's. Exhaust manifold bolts brake, this causes a ticking noise and exhaust leak. The 4th gens have a horrible cam design, doesn't get enough oil through the lifers so you will end up with lifter tick. I'm currently working on replacing struts on mine, the bottom strut bolt gets rusted and seized in the lower control arm bushing, its a very common problem, so you end up replacing that as well. I don't put a lot of miles on the truck, only other issues I have had have been a water pump going out and a shift solenoid going bad. Mine is a TRX4, basically the predecessor to the rebel. I hate the truck when I have to work on it but love it still. Great power, great off road. Mine had factory 17's and you will see that a lot of "off road" package trucks, don't worry about that, they do better off road typically then a 20" rim with a tire of the same diam. When my tires were shot, I upgraded to some factory 20's but only because I didn't like the chrome clad 17's and got a great deal on the 20's.
I can't tell you anything about the titan, but I have driven rams for the last 7 years. The 3rd gen rear end blew up, but that was literally the only non maintenance thing I had to repair. Drove it to 160 ishK, the 4th gen I didn't have to replace a cylinder head, whoever fixed the exhaust manifold bolt before me, didn't due it right, drilled it out and put in a helicoil, bolt broke and found out the drilled to far into the head and water was leaking.