Your much better off to look into a 3/4 ton for a 6000lb trailer. I pulled my 5000lb trailer with a 2002 5.3 with 3.73 rear axle and tow package and it worked, but not great. Bought an 06 2500 with the 6.0 and noticed a major difference in not only power, but over all stability. No more nerve racking sway when big rigs passd on the highway, or on windy days. Also, now, I moved up to a 5th wheel around 8000lb loaded and sure could not have done that with a 1/2 ton.
The old saying, you can never have too much truck is very true in most cases. I think you may be very dissapointed with a 4.8 as the engine will strain and the tranny will be stressed with that kind of weight.