98.5 thru 02 Dodge's with 24V Cummins.
Bodies and interiors are fair to good, some squeak issues but they can be addressed or ignored. Seats are comfy but tend to "give" with everyday use.
Motor, if you can keep the VP44 supplied with fuel it's not that bad, if you don't it will run you about $1300 give or take $100 to replace the injector pump. Upgrade parts are very plentiful and not that costly, thye also yield great results, this is a motor that likes to make power and seems to be really happy in the 350HP range as a daily driver or tow rig.
Tranny, a stock motor and auto tranny will last a long time, add more than a light upgrade to the motor you need to look at tranny upgrades soon as possible. As with the motor upgrades there are a bunchaton of folks offering upgraded trannies. The manuals are simply outstanding IMHO, the NV4500 and NV5600 are tough as nails and have proven themselves capable of withstanding some serious abuse. Only issues I know of is the fifth gear nut on the NV4500 and a weak stock clutch and 6th gear synchro on the NV5600. I have heard that towing with the NV5600 at 400+Hp levels is not reccomended, tends to be bad on the rear output bearing.
Axles and T-case, Dana 60 up front for all. Automatic trucks have a 70 rear. One tons use the 80 and the stick shift trucks use a 80 hybrid which is the center section from the 80 mated to roughly the same shafts and tubes as the 70. NP241 t-case, good unit and came in two different flavors, light and heavy duty, difference is the HD unit has a PTO out and a bit heavier chain assembly.
The front ball joints are known for failing often due to the poundage they are carrying, rest of the front end components do tend to wear out and cause a bad case of wanderlust LOL Most notorious is the tracbar, but again, there are fixes available.
Feel free to add to and/or correct this folks, all of the top of my head and others have different opinions.