Borancio

Hello every one, my truck shifts lock up at 34mph in normal driving, if i press hard the acelerator shifts better but inmediadly release the lock up, killing the motor rpm .
tranny has been completly overhall, ecu, has been tested and replaced by one operating fine.TPS, has been readjusted, several times by specification. My trans. Is a 340H, we check continuity, grounds, and voltage on wiring from trans. To ecu, cluster.
i herad that tcm are use in this truckd to control de trans., but i can't find where is the tcm located, already loock under center console, in fron of shifter and nothing was found, nor any wiring or plugs.
If somebody can help with this will be highly appreciatted.
Regards, Borancio