Just about every segment of the diesel market has made the upgrades necessary to meet tough 2007 emissions standards. Cummins recently announced that its popular motor home applications, including the ISX, ISM (shown), ISC, ISL and ISB engines, are also compliant. Changes include a particulate filter and crankcase ventilation system. The turbo has also been tweaked for improved response. The engine upgrades coincide with the complete switch to ultra-low sulfur diesel fuel a few months ago. I understand there was a rush in the trucking market to buy 2006 trucks before the changes were made. Buyers feared the new trucks would be more expensive, tougher to service and suffer reduced fuel economy. But I haven't noticed any change in motorhome sales, so perhaps that market isn't as fussy.