Heavy trucks can have the capability to record vehicle status and performance data. In many applications, this capability is intrinsic to the powerplant’s electronic controls. However little information has been published regarding Heavy Vehicle Event Data Recorder (HVEDR) data obtained from Mack trucks equipped with the V-MAC vehicle electronic control units. This study is focused on data from Mack trucks and the influence of wheel slip on the HVEDR-reported vehicle speed. Additionally, the influence of variables such as initial speed and loaded condition are discussed. A late model Class 8 Mack was instrumented with a calibrated data acquisition package (DAQ) and put through a series of tests so that the HVEDR data could be compared to the data collected by the DAQ.