Hi there, I'm a converted Ford truck person, so I do not know much about GMC. I'm dealing a 2010 4.0 V-6 Ranger for a 2008 Sierra 5.3 Z-71. Am towing a hybrid RV trailer that weighs about 4000 lbs. The Ranger struggles with this, hence the reason for switching to a Sierra. Would it be a struggle to pull this weight with a 4.8? There are some lovely extended and crew cabs at the same dealership, and somewhat less expensive. Also, would you hazard a guess at the rear axle ratio? Are there any other considerations that I haven't thought about? I'm not wanting to make the same mistake twice by purchasing an underpowered truck. Thanks, I appreciate your advice and expereience.