Keep the Cummins, and if it has the HO 24v (2004.5)... Absolutely keep the Cummins. Since you might occasionally tow a larger trailer, remember, "A bird in the hand is better than 2 in the bush."
I sold my 2004.5 2500 SLT QCSB 4x4 Auto 5 years after I bought it brand new, owing less than 10k...