Recently, I just purchase a 2008 TB (in line 6, 4.2) that sometimes exhibits engine run-on when shutting down from a cold start up (ie. morning start, pull truck out of garage, then shut off -> sometimes result in a second or two of run-on). Engine has 135kkm, don't know any history other than it appears to be well kept. Is this a common issue? Is it perhaps related to the Supplemental AIS system? I thought that in general with most of today's systems (computer and other things) that run-on was a thing of the past. Gas mileage appears to be in-line with "published" guidelines (ie. 14 /20 m). Possibly needs a cleaning of the throttle body / intake?? Thanks for any guidance in this area.