I'm going to assume that your machine has two pumps like most other excavators. That said, the pumps are set up to where one powers one track and a couple of functions, and the other powers the other track and the remaining functions.
Too they are usually designed where the two pumps tie together if you are traveling and using another function at the same time. One name for the valve that does that is the 'straight travel valve'. Basically it combines the pump flows so the one that would otherwise be carrying a track and the other function being used doesn't cause that track to lose flow and slow down, in turn causing the machine to walk to one side -vs- straight.
That said, try this test. Get your machine walking where you notice the weak track. Then hit another function (boom up usually works good because you can keep the lever pulled and not hurt anything). If you've got one pump section going bad then you should see the weak track gain power when the two pump flows combine. Given that you also have a problem with the swing, you could also walk the machine and swing at the same time. You should experience basically the same results doing this test, meaning the 'dead' track should see an increase in power, and you should have more power in the swing also. In either case you should see the increase in power with the combined flows, although you will probably also see a decrease in the speed of the functions due to the one pump handling the majority of the flow required......assuming that the problem is a bad pump.
I know for a fact this will work to test a bad pump because I used the same, basic, ploy to get a machine walked nearly a mile out of a pipeline right of way when one pump section went bad. Boom up, and hold the stick in that position to combine flows and keep them combined, and walked it right out with both tracks pulling.
I have tested, and had quite a few excavator pumps over the years so I have seen the problem your having along with quite a few others. As complicated and drawn out as it all sounds when I try to explain what to do, short of having a flow meter with the ability to put a load on the pumps this is about the only way I know to test a theory of a bad pump.
Hope this helps, and feel free to post again if you have any questions.