* E4OD: A four-speed automatic overdrive transmission. This was a very common choice.
* ZF-5: A five-speed manual transmission. This was also a popular option.
There might have been other less common options available depending on specific trim levels and ordering choices, but these two were by far the most prevalent. To know for sure which transmission is in a *specific* 1990 F-250, you'd need to check the vehicle's documentation (owner's manual, build sheet) or look at the transmission itself.