Pretty much all 99's will be 53 blocks. Nothing really to worry about, and if it does crack, Cummins will replace it.
On the 99's about the only engine thing to be concerned about it is lift pump pressure. Ask your Dodge dealer to do a PRESSURE test (not a volume test) and if the pressure is lower than 8 PSI at idle, ask them to 1) replace the lift pump and 2) warranty the injector pump for a year/20,000 miles. If the pressure is above 8 PSI, but lower than 13 PSI at idle, ask them to replace the lift pump and don't worry about the injector pump.
The other thing to be concerned about is the front end at 130K. I suspect it will be in need of ball joints. Replace them with Moog heavy duty components. They outlast the stockers by a long shot.
Other than that, the 99s were solid. Ignore the Chevy/Ford owners
I've run all three 3500 trucks (multiple years) and Dodge's running gear (with the exception of the front end) is second to none. It'll ride rough, but handle stutter bumps at speed better than the others.
Rod