common issues are leaks at transfer case to tranny and diff pinion seals. The pull is probably caused by a bent toe arm in the front-end. Not expensive to replace but obviously an alignment is required. Make sure the tranny shifts smoothly and the transfer case linkage is not seized up. Definitely put the truck in 4wheel drive and make sure everything is funtioning properly. Put the truck on dirt or gravel and try to watch if the front wheels are grabbing. Check the driveshafts for play in the u-joints and also try to look at the front axle shafts for u-joint issues.