Kick Panel should be it. my Other 89 Trooper has one located under the kick panel, ECM is under the console and I assume its the kick panel that houses the TCM.

Super


89'Isuzu Trooper LS 5 spd 2.6L
31" Big O X/T's
15x8 Eagle 058's
K&N Filter w/ Air Box Mod
2.25" DynoMax SuperTurbo
PolyUrathane/Indy4X Bushings
Suspension/ FrontEnd Tech/Hunter Certified Alignment Tech.