Best place I have found for ford diesels...

http://forums.thedieselstop.com/ubbthreads/

www.ford-trucks.com is another good site for info on chips.Search for Tony Wildman and DP Tuner,they're probably the 2 most respected chip programmers for Ford diesels.You'll need gauges,a freer flowing intake and exhaust before installing a chip.

SaddleSore

I had a 2000 F350 that I put a Superchip  65 hpTow chip in it. I added a Pyro to watch the exhaust temps. After a month or two, I added the larger exhaust because I frequetly hit the max temps when towing my trailer.

1st of all,  It's definately worth adding the chip for extra horsepower.

2nd Don't add the chip with adding the Pyrometer guage

3rd Budget to add the exhaust. You will probably need it.  My hottest temps where when I lugged the engine. It had plenty of power chugging along at 1800 rpm on a slow climb. The tranny would not downshift, But the temps would soar. Kick it down a gear and set some RPMs and the temps would immediately drop.

4th don't expect to see much difference in fuel enconmy.  You might see a slight improvement when you have a egg under the fuel pedal. But when you ask for the extra horsepower it comes with price tag for extra fuel.

The trend in todays trucks is to add a Tuner instead of a chip. I don't know the pro's or cons of a tuner for use with a 1999 7.3L  engine. Call several of the chip makers and ask their opinions.