David it varies by year and if it had A/C or not (i think).
On my 94 D90 with A/C the ECU is on the right side of the tub. I believe without A/C it would have located higher up directly in front of the passengers feet as shown in the pictures below.
On a 95 the ECU is under the passenger seat, and I think the same for the 97.
p.s. is your truck out of the living room yet?