Where was it mapped?
Who mapped it?
When you say you aren't happy, what aren't you happy with?
What does the AFR say on and off boost?
Has it been fitted and mapped as a standalone ECU controlling the gearbox and engine or piggybacked with the OEM ECU still controlling the gearbox?
What power are you running?
Have you done anything to the autobox?
I don't think I have ever heard of that ECU being fitted to a Supra on here but that isn't to say it's not up to the job. Full standalone ECUs I know of that are successfully controlling the autobox are Syvec & MoTeC for the J-Spec A340E and UK Spec A343E. For the tiptronic A343E (?) its only on a Syvecs but the MoTeC M150 would be up to the job if you wanted to pay for the R&D to be done.
Full standalone ECU forum favourites are Syvecs, Link, some run AEM, Apexi Power FC, HKS and a very select few MoTeC because of the cost. But the best is always expensive.
Piggyback wise it's pretty much GReddy E-Manage Ultimate or Blue but these are old tech now and not many map them. AEM do a nice piggyback but I don't know anyone running that.
Take a look here - http://www.mkivsupra.net/vbb/showthread.php?129455-Supra-ECU-Register