You've '89 7.3 but is it in a truck, van, bus/motorhome? In '89 I believe the vans and busses/motorhomes still had the c-6 and I think it was still an option for trucks too. If it's in a truck, do you have an overdrive cancel button on the panel to the right of the steering wheel below the tachometer? If you have the OD cancel button you have the e4od if not then it's a c-6. Either way, vacuum on these trucks is developed using a vacuum pump mounted to the belt accessories. I've never seen a vacuum regulator tied into the intake system on these trucks, if it is then maybe that is your problem although it might likely cause an engine run away as these engines like to run on any kind of oil, especially ATF.
How about a picture of the build tag in the door jam. That should have a code on it for the trans. Wait, as a new member you may not be able to post pictures yet, I can't remember but you can still look and tell us what it says.
