Zf5 is the model number of the 5 speed manual. That was used till 97. When superduty came out in 98 for the 99 model, it was changed to zf6 6 speed manual.
LOL that's taking the easy way out! Give these old idis a little bit of lovin and they can make some OK reliable power haha member here is around 400/750 on his 6.9l (I'll give exact numbers on it on the 18th we are having an idi dyno day....exciting I know) he has done more air/fuel mods and since last dyno and it has held it great