2005 used to haul 35oo lb trailer,2000 miles past 2 weeks. Toward end of trip harsh upshift despite mild acceleration, in nuetral no load, idle speed increased to 1100rpm without foot on throttle. After key shutdown for gas stops, idle RPM recovery to normal idle 800, normal shifts. Recurred again once since in subsequent 8 hrs of operation, now normal, no service engine light ever came on! thoughts? No other mechanical issues, unit has 55000 miles service per manual, Trans fluid pink, never overheated, Trans fluid recenlty replaced at 50000 Thoughts?? Throttle body failure eminent, if so where to find repair instructions.