Yea, you always have to disconnect the battery for 20 minutes or so. That clears the KeepAliveMemory (KAM) , specially after cleaning the MAF. When cleaning the MAF, the very first thing you do is disconnect the battery, -then clean. Just give a 1/2 hour or so, then reconnect the battery. That reboots the program.
BTW- I recall some guys getting those codes in the Mustang Forums with the Drive by wire systems. All they had to do is reboot. Like I said, it may work and it may not.
have covered other good possibilities. Simple stuff first, if that don't work,-go from there.
Wait, - You have a 2002 5.4L. I don't know why, but I was thinking you had a 3 valve. This isn't common with a 2 valve 5.4L, but you still have to reboot after cleaning the MAF. Revving up and shifting funny at highway speeds is usually a TPS problem. It goes MAF~TPS~Transmission as far as communication.
!! You soldered right to the sensor ? Yea, you can't do that with the TPS. Inside the TPS housing is ribbon wire, you most likley know what that is and yes you melted the ribbon soldering. The ribbon starts right after the terminal, then coils into a circle. So yea, it's right there.!! Replace that sensor for sure, -if you need a Pigtail, you can get those here http://www.fordparts.com/Default.aspx
and order from this Pigtail PDF catalog -
P0122 Throttle/Pedal Position Sensor A Circuit Low
P1122 Throttle Position (TP) Sensor Inconsistent With MAF Sensor Low Voltage
P1125 TPS Intermittant
So yea, something is wrong, -be it sensor, wiring or both. I think the sensor is wasted from soldering, because it wouldn't take that much heat to melt the ribbon and you still have an initial wiring problem within the MAF and TPS circuits. Check the MAF wires themselves/then circuit wiring. Check continuity, those damn wires can separate inside the insulation. Keep going, the problems there, you'll find it.
Keep us updated and feel free to keep asking questions.