The 4R100 from what I understand is about the same as the E4OD. I think one of the major differences is the way the torque converter locks up. On the E4OD, its either locked or unlocked. On the 4R100, it went from 0 to 100% lockup. The diesel version of the 4R100 was released in 99 with the new Super Duty's. I believe the gas version of the 4R100 was released with the 98 "F-250's" with the 5.4's. In 97 it was still the E4OD.

 

The easiest way to tell if you have the E4OD vs the C6 is whether or not you have a OD cancellation button on the dash (89-91) or on the end of the shifter **** (92-96 or 97 if you have the 250 or 350.) The E4OD replaced the C6, but I've heard of rare occurances of it showing up in later years. Same thing with the Manual transmissions. The T18 4 speed got replaced by either the M5OD in F-150's and LD F-250's, or the ZF 5 speed in the HD F-250's or F-350's, but I've heard of the T18 showing up in trucks as late as 1994, and swear they are factory. Who knows?!

 

Post a picture of it if you can. Look at the tag on the transmission on the driverside rear.

 

You could special order the C6 right up until 97, but I've only ever seen it with the 351 or the 460. Never with the PSD. So Sangetsu03 is wrong.