The TEC1,TEC3, and on correspond to Ford part numbers for replacement ECM/TCM units with specific strategy packages on them.TEC3 is printed on the ECM sticker with all the other info.
For example on my 04 the ECM/TCM is a "TBS6" unit that has VXBC9N8 and TQBF0NA strategies and they are crap. The power is way down from what is had new.
The last ones were VXBC7A3 and TQBE0AA before my latest reflash. They're crap too.
I don't know what the original strategies were on it new but it still didn't compare to my dad's 03.
Here's a link to a bunch of different ECM/TCM/FICM hardware part numbers and their 4 digit "control unit catchwords" and you will see how many different packages there are just for 2003.
2003 Ford F-series super duty firmware update database 
I would much rather have one of the TEC(X) strategy packages on my 04 truck any day of the week but I don't know how far backwards you can go with a particular ecm. That's another one for Bill to elaborate on I guess.