Early 99 so you have a smaller turbo... and smaller injectors then the later 99. Check and see if your intake horn has an AIH plug... if it doesn't then you definitely have an ealry 99. The early 99 only pulled air from the fender - not the front... so that's a good observation.
WIth the smaller turbo and injectors you're not going to see the 18psi that most on here do with their 99.5+ trucks... I'd be guessing but you'll likely see around 15 or so PSI. You basically have the same motor calibration as the OBS guys have so going by what they see if probably going to be your best bet to compare.
Maybe an OBS guy can jump in here and give us some baselines as to what he/she see's on their truck.