Matt, after 3 posts you can start your own thread.
Can you describe "bogged down" a little. You mean ground speed slows but engine rpm remains constant?
These hydrostats use charge pump flow to regulate the travel pumps, therefore correct transmission oil viscosity and a clean filter is vital. As the machine is new-to-you, I would suggest you start by draining the transmission oil and filling with the correct viscosity and replacing the transmission filter.
Search the forum for posts on cat hydrostats. Several people have been down this road before and a fair bit of advice has already been posted.
have you got a shop manual? if not check with Jensales.com for an oem shop manual. expensive but well worth the money. next make sure linkages are all adjusted properly. but I tend to agree with Cmark charge pressure may be the issue as it deals with the underspeed valve. The differences in oil pressure from charge pump will dump oil back to resivore and cause loader to stop just as if you had pushed the speed brake. I can scan and send you info on Charge pressure if you like as well as any other trouble shooting guides.