I think he is trying to move what he has on his lot. Not apples to apples comparison, but I had a 3.6L Grand Cherokee and currently have a 2015 Eco-Diesel Grand Cherokee.
The Eco-Diesel absolutely blows the 3.6L out of the water. The diesel pulls harder and accelerates faster than the gas engine.
I bought a new car in the middle of buying my house - just showed the lender that there was no impact to my payment. They're concerned with credit utilization