Ok. I finally got the information together, and here it is. Please respond in number to each question. If you have any notes or deviations from the included options that you believe are signifigant, please make a note. If you want to ask questions before posting, send me a PM.

1. What model do you drive Truck Shortbed, Truck Extended Cab, Suburban, Tahoe, Other (Specify):
2. Level 1500, 2500, 3500, 3500 dual rear wheels:
3. 4x4 or 2x4:
4. Driving Habits; 1 to 5 with 1 being conserative and 5 being a lead foot:
5. Tune of vehicle; 1 to 5 with 1 being perfect, 3 being average, and 5 as poor:
6. Fuel additive added every fillup in OZ; number or none:
7. Size of fuel tank (Suburban is 42 gal):
8. Rear Gear Size (3.23, 3.55, 4.10, ect):
9. Tire Size (ex; 245/75 R16):
10. Tread style; Offroad, Mud/Snow, Highway:
11. Gear vendor? (if so, od/ud ratio and how you use it):
12. Boost control; Mechanical/Electrical:
13. Boost pressure setting (4-20lbs):
14. Manual/Automatic Trans:
15. Thermostat (160, 180, 190, 195, 205, 215, none):
16. PCM programming (Heath 1.0, 2.0, Kennedy 72/76/max, Westers):
17. Timing Gear Y/N:
18. Intercoooled Y/N:
19. Mist injection Y/N:
20. Air filter (stock, stock w/ airbox mods, stock airbox with special filter, both, 97 and newer box, cone filter):
21. EGR/Non EGR:
22. GM Turbo Style (GM5,6,8, other):
23. Exhaust (Stock, mufff removed, kitty removed, 3", 3.5", 4", other)
24. TDC offset set to (stock, or the value you have it set to):
25. Stock injectors/High pop:
26. Synthetic oil Y/N:
27. Highway mileage (not towing, best averaged over 3 tanks):
28. When mileage data was obtained (Winter, Summer):
29. Approx miles on vehicle:

This is the items I could come up with that should affect mileage. I will store this data, and use graphs and a table to organize the data. If you have items on your rig that arent used in your calculation for mileage then make a note or don't include them (such as mist injection). I will report after we get enough data to start showing a trend.