I can't mix, bounce tracks, or run any signal through any bus without a large drop in amplitude in the target track. I've checked the routing setup, and can't find anything that would reduce the volume of the final output. Any help would be greatly appreciated.

Hi, and welcome to this forum. How do you route your project? Do you route everything to a master bus, or directly to Main Outs? Which plugins do you use in this project, and where? 
All the best.

You used the word "amplitude" (the power of the digital signal you measure with your meters) as opposed to "loudness" (the subjective experience of the sound power emanating from your headphone or speakers), so I assume that is what you mean. If you have checked your routing without finding the problem, and you want useful advice, you need to describe your routing in excruciating detail here, and it would be helpful to note the readings at each point in the route that can be metered. 

It is also helpful / useful to put your specs (Audio Interface, CPU, RAM, Motherboard etc) in your signature. It is done at the top of this page (and every other here, when logged in), under User Control Panel, Signature and comment. It will help diagnosing any, if any further issues.