You didn't say what type of 2500 Cummins you are looking to buy?
A 2500 in a 2 wheel drive, standard cab, long box will have about a 3000# payload vs a 4x4 crew cab which might only have a 2000# payload.
My 37ft fifth wheel had a 10500# shipping weight. Loaded, its over 12k.
Anyway, you can...