My 2014 SHO never had an issue launching, either brake boosting or just off the line in general. But my 2017 Fusion Sport has noticeable delay until it goes above 3k RPM. My N/A Explorer needs above 3k RPM as well. The key similarity in these 3 vehicle is the same 6F55 transmission, but the torque converters are different. The final drive is different as well, with the SHO having 2.77s, the Fusion Sport with 3.16s, and the Explorer with 3.65s - note that the 3.16 is the final drive for the SHO with the Performance Package.

I paid much closer attention the other day, by powerbraking to 2200 RPM on the Explorer and launching hard. I noticed the RPMs climbing to 2500 RPM or so but vehicle speed was not really increasing as fast until a certain point. My datalogs showed the throttle plate was open and no torque limiters/knock was in effect. It just seemed like it took awhile at 2500 RPM before vehicle speed and engine RPM started to climb. Is this a mechanical limit of the stock torque converter, or is there something else I could fix with tuning either the engine or trans? For the transmission experts, is this related to the stall speed of the converter since the TCC doesn't lock in 1st or 2nd on the 6F55?