The C6 was the automatic transmission put in the majority of these trucks. With just 3 speeds and no lock-up torque converter it wasn't particularly efficient, but it was robust and effective.
The C6's in 4x4 trucks had a deeper pan and, therefore, a need to pull the fluid from the bottom of that pan to do that. So, there was a suction tube added, shown as # 7A102 in the illustration below.
And, here's the whole part number - D3TZ 7A102-C. I've added a note in my catalog saying that I think this applies not only to the E150/350 and U150 4wd's, but also to the F150/350 4wd's. In fact, I wasn't aware that the E's came with 4wd, as the listing for C6 pans, below, shows only the F & U series got the 4wd deep pan. So, I believe the "E" for the E150/350 should actually have been "F".