In these transmissions (I am assuming you are 5R55E, but it is equally true in the 4R44 and 4R55) generally troubleshooting consists of checking for electrical faults and then mechanical faults.
By the way.. a 4000 rpm shift is a good way to break a band... be careful.
Anyway... in the "perfect world" you would want to isolate the problem as being IN the transmission, and not because the computer is not sending the correct info. FORD has various tools to enable you to do this, but they are not something the usual home mechanic is going to have (transmission tester, NGS tester, SBDS, WDS etc). Once you have isolated the problem as NOT being related to the computer, your attention turns to the trannie itself. Two possible culprits are the 1-2 shift valve (which could be getting stuck until jarred loose under high pressures) or is could be the shift soelnoid C is sticking, or for that matter it could also be the EPC solenoid. In other words, we're more than likely talking valve body problems.
Soo...my advice - in the less than perfect world of the home mechanic without all the fancy stuff? Swap in a known good VB (using new gaskets) and see if that doesn't cure your problems. If you are thinking of doing this and the fluid ya got is old... do a flush before you do the swap out.... you'll lose a few quarts that way when you drop the pan full of clean new fluid but you won't potentially be gunking up your replacement VB. While you are in there go ahead and replace the filter too.
