Well first and foremost something is WRONG for the driveshaft to be out.. either bad t-case, or front diff.. I would defintely ask more questions a/b this...
As for as an early 99 or 99.5 "most" of the time like i said "most" the early 99 had the powerstroke emblem on fenders. look at my avatar (pic on profile) and that'll s/how you where its located. also look at manufactor date. if made prior to 12/8/98 ( i believe thats the cutoff) its an early 99 model
The early models had ALOT of differences than the 99.5 ie smaller turbo's, different injectors, different hpops, etc. there is a sticky at top of early 99 page that will tell you everything..
But look at the Manufactor date inside driver door on cab and get the date and that'll tell you which you have.
All that said welcome to the forum. These trucks are GREAT as long as you maintain them. The mileage on yours is low which is a good thing because these things will run forever.. my buds excursion has 585 or 595,000 miles on it and runs just as strong as mine..
Once again welcome to the forum and post some pics as soon as you can..