What are you pulling it with? It might be less a question of fuel savings and more a question of possibility. My last truck was a 2005 GMC 1500 2WD with the 5.3 and 4spd tranny. I forget what gears it had, but it got good mileage so high gears. It would pull a flatbed or car hauler loaded to the max with no problems. I used it to pull machine tools, sometimes up to 10,000lbs. No problem. Then one day my boss asked me if I could pull the company box trailer (little trailer) 300mi to Louisiana because he couldn't find a hotshot available. The load inside was <2,000lbs. First time I had ever pulled a box trailer. My truck did NOT like it one bit. Pulling that flat front down the interstate at 65mph was like trying to pull a parachute. The truck was continually shifting between 3rd and 2nd gear at 65mph and my dash said I was getting 7.5MPG where I normally would get 18-22MPG. I had to stop for fear of destroying my transmission. Had to call my boss and tell him I wasn't able to do what he wanted. He ended up finding a hotshot to meet me and take over. Hotshot was driving a dodge 2500 with a Cummins and I spoke to him afterward and he said his truck pulled it like it wasn't there. It didn't affect his MPG at all. Same MPG as unloaded (nearly 20mpg). As much as it has to do with the gearing and the low end torque of a diesel, I think it had to do with the profile of the truck and the amount of exposed trailer. My GMC factory ride height was pretty low, and the truck was not tall either. It had pretty low cross sectional area for a truck and a low coefficient of drag, and it was designed that way and that's why it got good mileage. That box trailer behind it stuck up 2+ft higher than the cab of the truck and caught all the wind. The dodge truck had a higher ride height and a taller cab. Overall bigger truck, more cross sectional area, and it totally blocked all the wind that would have otherwise hit the trailer. The trailer rode in a nice little sheltered air bubble behind his truck and didn't cause much resistance at all. So for him, it probably wouldn't have mattered at all whether it was flat front or v-front. For me, it wasn't possible to pull the flat front, but it may have been possible to pull a v-front. I don't know; never tried, and I don't have the truck anymore to test it. I have a 2010 GMC Yukon now and I've pulled that very same box trailer with it, with no issues. It has the same 5.3 engine but a 6spd transmission and it has much more cross sectional area. The trailer is mostly hidden behind the yukon.
I say all that to say this; if you've never pulled a box trailer with the truck you are intending to use, maybe you should try it out.