My truck & my bro's 68 Hurst Olds

 

My '06 rclb V6 5 speed averages about 18-19 mostly city driving. I have been able to get damn near 23 on the highway. I have a 3.23 gear, stock wheels/tires and a tonneau cover.
The V6 is fine for a DD, but if you can help it, try and get a V8. They get about the same if not better mileage and you have WAY more power to tow/haul or just for fun.
And as far as that truck being a good deal, I think it's about what they are going for, nothing special.

 

I have a 07 rcsb with the 4.8 and a couple of mods, and I can average pretty close to 23 highway doing 70-75 with 300 pounds of tool to help.