If you prefer the gas then go with it.
I had a 2011 F350 with a 6.2 and 4.30 and I was towing a Arctic Fox 27-5L with a 13,400# GVWR and it just fine. We lived in MT at that time and towed the mountains and never had a problem. Sure we went a little slower but still passed the semis on the passes.
When we went to Alaska with the same truck and a Northern Lite 10.2' CD Special Edition truck camper and traveled over 11,000 miles. I averaged 10.88 MPG hand calculated over the whole trip, I didn't figure that was to bad for a LB CC King Ranch F350 with almost 4,000# truck camper.