I have a TEK2 made by Power Engineering on june/2002.
Must I go to the same company to get a TEK3 or can I go where ever I want to get it done?

I don't think that PE will do individual maps anyway!
You may find that the original Tek2 won't be recognised as a 'trade in' type thing though, so will need to pay as if from scratch (this is what I found when I looked into it, but it may have changed & certainly changes from mapper to mapper!) But if that is the case, you can just flog the Tek2 & get a plain 802 or whatnot in return & have that mapped, so it doesn't make much of a difference!

I had a tek2 from PE and Tek3 from BRD..no problem

I heard from EcuTEK that if I bought my ECU from them, then I can go to what ever company I choose. I´m really stuck here. Don´t want to pay for another TEK2 + remapping just to get a TEK3.

T.J, when did you get your TEK2?