Here are you truck numbers, YTD, for CY 2012:
Ford F-Series: 350,455 (+11.9%)
Chevy Silverado: 223,480 (+3.5%)
GMC Seirra: 84,050 (+4.5%)
Total GM: 307,530
Sources:
http://media.ford.com/images/10031/July12sales.pdf
https://www.media.gm.com/dld/content..._July_2012.pdf
As for the Ecoboost, it gets slightly better mileage than the 5.0, but kills it in low-mid rpm power (which is where a truck needs it). It also gets better mileage than a 5.3L Silverado, but makes more HP and far, far more low-mid range torque. GM's 6.2 makes more HP than the Ecoboost, and the same torque (though at a much higher rpm), but its MPG is much worse.