I'll comment on the 4.8 vs 6.0
I have a 2001 pickup ext cab with the 4.8. and a 2005 Chev based 2006 Pleasure-Way Lexor. it has the 6.0.
They both have the same transmission, the rear end ratios differ
the 4.8 will have about 270 HP
the 6.0 will have about 305 HP
on the pickup the 4.8 is fine for most driving.
For hauling or up grades the engine is marginal and downshifting is usually required...if left in OD, the transmission will "hunt" shifting back and forth between OD and 3rd constantly. I have never towed with this truck- I just don't think it has the nuts.
typical mpg for this truck is about 17 or so. We have 160,000 miles with only a water pump replacement required on the motor- otherwise gas, oil, filters, spark plugs and a fuel pump.
The 6.0 in our van is sized very well for the much higher weight ( and wind load), the 6.0 ain't a racer but it has plenty of torque. I find the motor and tranny are perfect for this application. Our MPG at 65 MPH is about 15. On 6% downhill grades, shifting manually to 3rd will hold near a steady 55 MPH, saving the brakes
We also have 5000# towing capacity
I don;t think that a 4.8 is the correct motor for the weight of a class B...and in practicality a 4.8 may actually get less MPG as it may be straining and the spark timing will not be able to fully advance ( which is key to economy).
Our record with the 4.8 is really very good, but I would not buy another pickup with the small v8. Having driven my Pal's same truck with the 5.3, his is better all around hills, grades, hauling and trailering.
mike
