I have a 08 F-350, it has 32000 miles on it and my 3/36 just ran out on time 8/27. 2 weeks ago coming down a 6% grade in tow/haul mode pulling my toyhauler (12000 lbs or more) i was in regen mode and when my engine brake engaged i heard like a thumping sound (kinda like i had a flat front tire)...