Funny that you ask. The highest I have ever seen is 827. 7 miles on my 4x4. I filled up on the East side of Huntsville, Alabama and drove back home and around Northwest Arkansas for a couple days. I ran out at 827. 7. (I planned to run out and had fuel in the back of the truck) I ran out at exactly 90 miles after the DTE reached zero. When I filled up the completely empty tank, including 100% of the reserve area, it took 42. 34 gallons. The manual says it's 35. The reason I got such good mileage on this trip is because I drove it nearly non-stop on the Interstate at 60mph. The truck gets awesome mileage right there and there were no mountains and I wasn't towing. It was a test to see what I was capable of getting.
For your reference, the pasted data below is what I recorded starting with the tank I mentioned above. The first column is the number of miles on the tank. The second is how many gallons it took to fill it afterward. The third column shows what the overhead MPG readout is. Fourth is the hand calculated MPG. The last column is how far off the computer was.
My computer WAS ACCURATE before I put my fueling boxes on the truck. They "fool" the computer, so it can no longer accurately figure my mileage. In the numbers listed below, speeds varied, some were interstate trips, others were city driving, but none of the figures were while towing. I have a 2004 with the 305 / 555 engine, 4x4, and 35" tires.
I hope this data below is useful for somebody somewhere, because it was a ***** to get it posted!
<table border="1" id="table3" cellspacing="1"> <tr> <td width="121"> Mile on Tank </td> <td width="79"> Gallons </td> <td width="72"> OHC MPG </td> <td width="78"> MPG </td> <td> OHC Error </td> </tr> <tr> <td> 827. 7 </td> <td> 42. 34 </td> <td> 24. 8 </td> <td> 19. 55 </td> <td> 5. 25 </td> </tr> <tr> <td> 610 </td> <td> 34. 59 </td> <td> 20. 3 </td> <td> 17. 64 </td> <td> 2. 66 </td> </tr> <tr> <td> 499. 1 </td> <td> 27. 2 </td> <td> 19. 5 </td> <td> 18. 35 </td> <td> 1. 15 </td> </tr> <tr> <td> 687. 5 </td> <td> 37. 792 </td> <td> 22. 9 </td> <td> 18. 19 </td> <td> 4. 71 </td> </tr> <tr> <td> 154. 8 </td> <td> 8. 696 </td> <td> 21. 7 </td> <td> 17. 80 </td> <td> 3. 90 </td> </tr> <tr> <td> 565. 4 </td> <td> 36. 548 </td> <td> 19. 3 </td> <td> 15. 47 </td> <td> 3. 83 </td> </tr> <tr> <td> 567. 1 </td> <td> 35. 671 </td> <td> 20 </td> <td> 15. 90 </td> <td> 4. 10 </td> </tr> <tr> <td> 583. 8 </td> <td> 35. 773 </td> <td> 21. 5 </td> <td> 16. 32 </td> <td> 5. 18 </td> </tr> <tr> <td> 588. 3 </td> <td> 34. 3 </td> <td> 20. 9 </td> <td> 17. 15 </td> <td> 3. 75 </td> </tr> <tr> <td>
546. 2 </td> <td> 35. 69 </td> <td> 18. 3 </td> <td> 15. 30 </td> <td> 3. 00 </td> </tr> <tr> <td> 564 </td> <td> 34. 191 </td> <td> 18. 7 </td> <td> 16. 50 </td> <td> 2. 20 </td> </tr> <tr> <td> 401. 6 </td> <td> 27. 051 </td> <td> 17 </td> <td> 14. 85 </td> <td> 2. 15 </td> </tr> <tr> <td> 623. 4 </td> <td> 37. 22 </td> <td> 19 </td> <td> 16. 75 </td> <td> 2. 25 </td> </tr> <tr> <td> 638. 7 </td> <td> 37. 9 </td> <td> 19. 2 </td> <td> 16. 85 </td> <td> 2. 35 </td> </tr> <tr> <td> 332. 8 </td> <td> 19. 68 </td> <td> 19. 2 </td> <td> 16. 91 </td> <td> 2. 29 </td> </tr> <tr> <td> 472. 1 </td> <td> 25. 286 </td> <td> 21. 4 </td> <td> 18. 67 </td> <td> 2. 73 </td> </tr> <tr> <td> 618. 1 </td> <td> 36. 297 </td> <td> 20. 3 </td> <td> 17. 03 </td> <td> 3. 27 </td> </tr> <tr> <td> 624 </td> <td> 37. 715 </td> <td> 19. 7 </td> <td> 16. 55 </td> <td> 3. 15 </td> </tr> <tr> <td> 598. 7 </td> <td> 35. 773 </td> <td> 20. 2 </td> <td> 16. 74 </td> <td> 3. 46 </td> </tr> <tr> <td> 703. 7 </td> <td> 36. 656 </td> <td> 22. 2 </td> <td> 19. 20 </td> <td> 3. 00 </td> </tr> <tr> <td> 683. 5 </td> <td> 43. 38 </td> <td> 18. 3 </td> <td> 15. 76 </td> <td> 2. 54 </td> </tr> <tr>
<td> 646. 9 </td> <td> 36. 648 </td> <td> 20. 8 </td> <td> 17. 65 </td> <td> 3. 15 </td> </tr> <tr> <td> 535. 3 </td> <td> 31. 85 </td> <td> 19. 3 </td> <td> 16. 81 </td> <td> 2. 49 </td> </tr> <tr> <td> 719. 8 </td> <td> 43. 032 </td> <td> 20. 6 </td> <td> 16. 73 </td> <td> 3. 87 </td> </tr> <tr> <td> 648. 2 </td> <td> 38. 605 </td> <td> 20 </td> <td> 16. 79 </td> <td> 3. 21 </td> </tr> <tr> <td> 585. 6 </td> <td> 36. 534 </td> <td> 18. 8 </td> <td> 16. 03 </td> <td> 2. 77 </td> </tr> <tr> <td> 572. 5 </td> <td> 38. 68 </td> <td> 18. 6 </td> <td> 14. 80 </td> <td> 3. 80 </td> </tr> <tr> <td> 607. 5 </td> <td> 39. 41 </td> <td> 19. 5 </td> <td> 15. 41 </td> <td> 4. 09 </td> </tr> <tr> <td> 566. 3 </td> <td> 38. 47 </td> <td> 20. 1 </td> <td> 14. 72 </td> <td> 5. 38 </td> </tr> <tr> <td> 609 </td> <td> 37. 17 </td> <td> 20 </td> <td> 16. 38 </td> <td> 3. 62 </td> </tr> <tr> <td> 627. 7 </td> <td> 36. 72 </td> <td> 20. 8 </td> <td> 17. 09 </td> <td> 3. 71 </td> </tr> <tr> <td> 561 </td> <td> 32. 716 </td> <td> 21. 5 </td> <td> 17. 15 </td> <td> 4. 35 </td> </tr> <tr> <td> 720 </td> <td> 36. 772 </td> <td> 23. 3 </td> <td> 19. 58 </td> <td> 3. 72
</td> </tr> <tr> <td> 180. 2 </td> <td> 8. 91 </td> <td> 25. 5 </td> <td> 20. 22 </td> <td> 5. 28 </td> </tr> <tr> <td> 629 </td> <td> 37. 858 </td> <td> 20. 6 </td> <td> 16. 61 </td> <td> 3. 99 </td> </tr> <tr> <td> 632. 4 </td> <td> 38. 377 </td> <td> 20. 4 </td> <td> 16. 48 </td> <td> 3. 92 </td> </tr> <tr> <td> 736. 2 </td> <td> 37. 568 </td> <td> 21. 5 </td> <td> 19. 60 </td> <td> 1. 90 </td> </tr> <tr> <td> 556. 1 </td> <td> 36. 553 </td> <td> 21. 3 </td> <td> 15. 21 </td> <td> 6. 09 </td> </tr> <tr> <td> 482. 9 </td> <td> 28. 391 </td> <td> 21. 7 </td> <td> 17. 01 </td> <td> 4. 69 </td> </tr> <tr> <td> 619. 1 </td> <td> 35. 962 </td> <td> 21 </td> <td> 17. 22 </td> <td> 3. 78 </td> </tr> <tr> <td> 609. 3 </td> <td> 38. 2 </td> <td> 19. 7 </td> <td> 15. 95 </td> <td> 3. 75 </td> </tr> <tr> <td> 463. 5 </td> <td> 27. 724 </td> <td> 20. 4 </td> <td> 16. 72 </td> <td> 3. 68 </td> </tr> <tr> <td> 596. 9 </td> <td> 36. 494 </td> <td> 19. 7 </td> <td> 16. 36 </td> <td> 3. 34 </td> </tr> <tr> <td> 440. 8 </td> <td> 25. 758 </td> <td> 20. 4 </td> <td> 17. 11 </td> <td> 3. 29 </td> </tr> <tr> <td> 596 </td> <td> 35. 74 </td> <td> 19. 5 </td> <td> 16. 68 </td> <td> 2. 82
</td> </tr> <tr> <td> 612. 1 </td> <td> 38. 278 </td> <td> 19 </td> <td> 15. 99 </td> <td> 3. 01 </td> </tr> <tr> <td> 631. 1 </td> <td> 37. 629 </td> <td> 19. 9 </td> <td> 16. 77 </td> <td> 3. 13 </td> </tr> <tr> <td> 660 </td> <td> 41. 267 </td> <td> 19. 3 </td> <td> 15. 99 </td> <td> 3. 31 </td> </tr> <tr> <td> 563. 1 </td> <td> 34. 5 </td> <td> 20. 4 </td> <td> 16. 32 </td> <td> 4. 08 </td> </tr> <tr> <td> 643. 3 </td> <td> 38. 34 </td> <td> 20. 3 </td> <td> 16. 78 </td> <td> 3. 52 </td> </tr> <tr> <td> 629 </td> <td> 38. 863 </td> <td> 19. 9 </td> <td> 16. 19 </td> <td> 3. 71 </td> </tr> <tr> <td> 644. 4 </td> <td> 35. 809 </td> <td> 22 </td> <td> 18. 00 </td> <td> 4. 00 </td> </tr> <tr> <td> 653. 2 </td> <td> 38. 815 </td> <td> 20. 2 </td> <td> 16. 83 </td> <td> 3. 37 </td> </tr> <tr> <td> 731 </td> <td> 37. 724 </td> <td> 23. 5 </td> <td> 19. 38 </td> <td> 4. 12 </td> </tr></table>