Axle codes are on the door sticker. In reality, any gears will tow the trailer you have just fine. I have 3.55 gears in mine, and it tows my 6500# trailer remarkably well.
The EB is easily my favorite 1/2 ton powertrain right now. My '11 has been great thus far. 17.7 mpg lifetime (including towing), lots of power, just a great truck. I have had to replace the blender door or blender motor or something (800 miles out of warranty!), but that's been the only hiccup so far.
Good luck.
2008 Hornet Hideout 27B
2010 Chevy Suburban 1500 LT, Z71 package, 5.3/6A/3.42
2015 Ford F150 XLT Supercrew, 2.7 Ecoboost/6A/3.55 LS
Prior TVs:
2011 Ford F150 Ecoboost 3.5
2006 Chevy Silverado 2500HD Duramax LBZ
2005 Chevy Suburban 1500 4x4 LT, 5.3/4A/4.10