I've got a 2006 starblazer. Mpg is not great, 20 Max but a lot depends on the load you are carrying. I'm going from Essex to Matlock this weekend and the round trio will cost me £60-£70. Nice van though if you can cope with the eberspacher heater which drives me mad at times
MPG has only recently been covered in an earlier thread
Lots of examples, including mine, are on there. I run a 2.8 Coach Build hi line and av 25.18. Best is 34.91, worst is 22.12. All depends on the weather, high winds etc and of course, how heavy your right foot is and how you drive it
Download the app MPG Calc and start to monitor your own fuel usage. Very helpful app. It's covered in the link below under my post as PP Bear.
This link will take you to the post. Hope it helps