Seems about right. 6,000 RPM would give you a little over 150 mph and that is were the factory limit is set..
Maybe some one else can check out on the road today. I think the final drive ratio is the same with the manual and auto transmissions and you are not driving a SRT6 by the speedometer gauge top end of 160 mph.
Driving those speeds should give you about 27 ~ 28 miles per gallon if you can put it in cruise control and have an open road.