If the truck is made between 94 and 97 with an automatic it will have an E4OD transmission. If it is made between 99-03 it will have a 4R100. The gearing in the 94-97 was anywhere between 3.50 to 4.10 gears, you will have to crawl under the truck and read the axle tag. Most 99-03 single rear wheel trucks were 3.73 gears and the duallies had 4.10 gears.
No need for a number on the trans, just the year it was made like I mentioned above.
Good luck, you will love the 7.3 powerstroke.