The Ultra Max as the Cargo Max are built on the longer and heaverier 12,300 lb gvw Motorhome cutaways...the 4.8 is NOT available on that chassis at all...now, with the 6.0 the 6 spd trans and the 3:73 axle ratio, i would not be afriad to think that that setup after it has a good 10,000 mile on...