Not sure if it's been said, but many ECUs at WOT have a bypass loop. This could be kicking-in your stock-ish tune at WOT, or at least, compensating for a POOR tune.
I agree with what others have said - If a tuner cannot produce a tune that works, they did not produce a tune. Period. Get a refund or slam that mother****er all over the forum.
That said, the ONLY person I would let touch my truck, were I to mod it, is a man named Tim Bailey.
I'm not sure if he still owns Surgeline Tuning, but he also worked for Cobb (a huge import tuner) whi is now in Austin, TX.
DO not give-up, and do not drive her hard until the tune matches the mods correctly.
*Are you using a stock MAF? How is the condition of the MAF sensor?
*Do you have an oiled air intake?
*PM me with your mod list, and I'll see if I can't dig-up Tim's number. He turned a lowly 2.5 liter Subaru of mine into a Porsche-eating beast. And my AFRs were always silky sweet, even with all my mods installed by myself.
IF A TUNER WON'T STAND BEHIND HIS TUNE(S) then F*** him!
-Big