if there is a cable from the transmission to the throttle body it is a 700R4.if there is a huge electronic plug in behind a plate next to the exaust on the passenger side of the trans it is a 4L60E.
The 88-98 Chevy GMC trucks used two automatic overdrives the THM700R4/4L60E. the THM700R4 was used from 88 up till 92 then switched to the 4L60E wich is basically the same transmission but used an electronicly activated valvebody controlled by the engine controll module. The 700R4 can be found in many other GM vehicles from f- bodies (camaro/trans am) to the corvette, and both contain an electronically activated "lock up torque converter" wich lowered cruising speed rpm's...
In 1990, the Turbo Hydra-Matic 700R4 was renamed the 4L60. Under the new designation, the "4" stands for the number of forward gears, the "L" for longitudinal applications (rear-wheel-drive), and the "60" is the strength rating (less than the 4L80)."60" is the relative torque value. For example, 80 is stronger than 60, which is stronger than 40, etc. A 4L80-E can handle more torque than a 4L60-E. The "E" denotes electronically controlled shifting. The 4L60 however is hydraulically shifted based on governor pressure and TV cable position. 1992 was the last year of widespread usage of the 700R4 (4L60). 1993 Camaro, Corvette and Typhoon were equipped with the last production 700R4. The last design change of the 700R4 was an added checkball to the valve body.
In 1992 electronic controls were added, and it became the 4L60-E.The 4L60E went into service in trucks, vans, and SUVs in 1993 and in all RWD passenger cars (Corvette, F and B/D bodies) in 1994.