My current truck derives its power brakes from a vacuum assist which is taken off of the power steering pump.
No, your '99.5 Ford diesel uses hydraulic assist which is taken off the hydraulic pump, which some folks mistakenly call the power steering pump. IOW, your truck has hydroboost power brakes. But you're right, diesel engines don't make vacuum so your '99.5 also has a small vacuum pump to make the vacuum power needed for the HVAC doors and other vacuum-powered systems, such as ESOF if you have it. But the small vacuum pump is not big enough to also create enough vacuum to operate vacuum power brakes.
The new trucks with vacuum power brakes have a much bigger vacuum pump than your truck. And they have a smaller hydraulic pump that supplies only the power steering, so it's okay to call it the power steering pump.