E450 What transmission do I have?

Behind the V10, the 4R100 torque converter is normally locked at cruising speeds regardless of gear. There's only a very small range of throttle travel where it will stay in top gear and unlock, this way it doesn't generate too much heat. When it downshifts, it unlocks for the downshift then re-locks. The time required to re-lock depends which gear it downshifts into. i.e. 2nd gear will take locker to re-lock after a downshift. I believe that is done to maximize HP for passing. The diesel version of the 4R100 stay unlocked much more. I had always assumed it was to compensate for the narrow HP-band of the 7.3L however Mark K. indicates it might have been simply due to a programer who didn't know any better. That T/C strategy is why the 7.3L eats through transmissions while they are generally lifetime items behind the V10.

I'm not sure how the 5R110 torque converter clutch strategy works.