When I had the 275's and the EZ and towing about 4k over passes and city driving 800 miles a week I was getting about 13-14 MPG. When I went to the DD2's I now get 11. 5-12 MPG. I have never got below 11MPG EVER. Empty with the 275's and EZ I got around 21-22 driving nice .
When I put the DD2's in I now get around 19-20. This is done by hand calcualtions not off the trip computer.
You will not notice a huge difference going from complete stock to 275's if you DONT tow. If you do tow you will notice a difference. Your mileage will go up as well, at least it did for me.
If you want to see some gains from Stock in HP go for no less then DD2's. If you want to go the injector route. If I could do it over I would go 275's and Comp box. The price of DD2's are over 2 times as much as 275's and IMO are not worth the extra $$$. Others may think differently. But me going from 275's to DD2's It wasnt a huge jump in power for the $$$$. My 0-60 times with the 275's and comp on 5x5 was 6. 54 Sec. With the DD2's and box on 5x5 my time dropped to 5. 84 sec. (pretty dam fast for a 7k LBS truck) Over a half second drop not bad at all, but prepare to lay down some smoke to get those times.
If your completely stock get a EZ box first. This is the most single best bang for your buck. It just plugs in and your done in 5 min. Injectors take time and and some mechanical experience.
I hope I have answered some questions, if your in my area feel free to give me a call and try my truck out.

You will not notice a huge difference going from complete stock to 275's if you DONT tow. If you do tow you will notice a difference. Your mileage will go up as well, at least it did for me.
If you want to see some gains from Stock in HP go for no less then DD2's. If you want to go the injector route. If I could do it over I would go 275's and Comp box. The price of DD2's are over 2 times as much as 275's and IMO are not worth the extra $$$. Others may think differently. But me going from 275's to DD2's It wasnt a huge jump in power for the $$$$. My 0-60 times with the 275's and comp on 5x5 was 6. 54 Sec. With the DD2's and box on 5x5 my time dropped to 5. 84 sec. (pretty dam fast for a 7k LBS truck) Over a half second drop not bad at all, but prepare to lay down some smoke to get those times.
If your completely stock get a EZ box first. This is the most single best bang for your buck. It just plugs in and your done in 5 min. Injectors take time and and some mechanical experience.
I hope I have answered some questions, if your in my area feel free to give me a call and try my truck out.