1934 was the first year for IFS in CARS... if you want to get technical, and consider the 1939 "coupe pickup" to be a light truck, then that would be the first year.

The ElCamino was also based off a CAR suspension, which would be 1959.

Here is a good web site:

History of Chevy Trucks


Another quality post.
Real Trucks Rattle
HELP! The Paranoids are after me!