Working on my 2018 Explorer XLT w/ the 6F55 (N/A 3.5 V6 not a whole lot of torque). I think the source of the laggy shifts is these 0.5 second events. Torque source is "Trans Shift Mod". Throttle plate isn't closing. Spark is being reduced. Before the shift it is 24* and cuts down to 3* advance.
Looking at my SHO and Fusion Sport datalogs, those 6F55 don't have this long of a delay in between shifts.
Is this due to the upshift torque reduction or something else? The N/A V6 makes less torque at the WOT shift points and I don't think it needs any torque reduction. This same trans is used on EcoBoost applications making 300-400 ft-lb at the shift points, and this N/A barely makes 200 ft-lb at the shift point.