See Figures 1 and 2
The Turbo Hydra-Matic 700-R4 (also known as the 4L60 on models through 1992) and their electronically controlled cousin the 4L60-E (1993-96) 4-spd automatic transmission serial numbers are located on the rear right side of the transmission case, above the oil pan.
The THM 700-R4 (also known as the 4L60) was used in these models from 1985-92. It is a fully automatic transmission which provides 4 forward gears and a reverse gear. The oil pressure and shifting points are controlled by the throttle opening, via a Throttle Valve (TV) cable.
Beginning in 1993, the 4L60-E (the new suffix stands for an electronically controlled version of the old transmission with the same name) replaced the its older cousin. Like the THM 700-R4, the 4L60-E is a fully automatic transmission providing 4 forward gears and a reverse gear. But unlike the older version, shift points are controlled by the engine or powertrain computer control module through 2 shift solenoids. The unit also utilizes and electronic Torque Converter Clutch (TCC) so the torque converter can operate as a direct link between the flexplate and the input shaft during high speed vehicle operation.