Well feel luck on the No Cat. I have a 99 Automatic and it has a Cat.

Chet

 

Differences in the E99 suspension:

Smaller diameter sway bars.
Different swaybar endlink bushings.
U-bolts on front suspension are flat at the u-bend.

Can't think of anything else.

Here is a very comprehensive list of differences:

Some differences between Early 99 and 99.5+

Credit to Chase (aka superduty4x4), Ron aka (Ron's Power Stroke) and in Bold credit to Jet (aka SolidGround) RIP.

It I did not credit everyone envolved with this I apologize.
Early 99 has a wicked wheel stock from the factory. And much smaller turbo (spools faster, though)

The early99 has 120cc(AB code) injectors and the late99-03 has 140cc(AD code) injectors.

The early99 has 2" intake runners. The late99-03 has 3" intake runners.

The early99 has a 15° swash plate HPOP. The late99-03 has a 17° swash plate HPOP.

The early99 has one glow plug relay. The late99-03 has one glow plug relay and one air intake heater relay side by side. Both relays are above the passenger side valve cover toward the front of the truck.

The early99 has a totally different air filter that is not inter changeable with the late99-03 (except for DRW trucks) . But you can put the late99 air cleaner assembly in the early99 truck.

The early99 track rod has smaller mounting bolts than the late99-03. (except for DRW trucks)

The early99 has shallower rotors than the late99-03. (except DRW trucks)

The early99 has shorter hub-bearings than the late99-03. (except DRW trucks)

The early99 front axle U bolts are square where they go over the spring pack. The late99 U bolts are round. (except DRW trucks)

The early99 has a different pitman arm than the late99-03. (except DRW trucks)

The early99 does not have the AIH like the late99-03.

The early99 does not have the automatic transmission fluid cooler in the radiator.

The early99 has no indicator light showing that "cruise" is on. Late99-03 has a cruise light that will come on when you set the cruise control. The early99 truck has the light in the dash already (not always). A newer PCM(Yes it will plug in and will run better too) must be used to make the cruise light illuminate. It is a green light on the right side edge, half way up.


There will be exceptons depending what month in 1998 or 1999 it was built.

 

Here is an interesting document that talks about the 1999.5 engine updates.
It doesn't list the the front cover HPOP reservoir gasket change since that happened much later in the model year.