Walk behind Weak self propel HRB217TDA MAEA 1016626 3 spd

Where do I start on evaluating this mower for weak self propel in all 3 speeds. Wheels & drive gears seem to be ok. I am thinking belt, then crankshaft pulley and finally a transmission gear worn out. What else? It is about 14 years old and still in very good shape with composite deck. What typically wears out on these? Can I get individual trans gears if I pull trans apart?

I ran into a similar situation.Mine was progressively getting slower. I checked the basics like cable adjustment, and gave it a good look over. I suspected it was low on fluid, even though I never saw any telltale signs of a fluid leak. I ended up pulling the transmission as there is no way to check it on the mower. Sure enough it was low. After doing some research and looking locally and not being able to source any Genuine Honda oil, I topped it off with ATF and put it back together. It lasted until the end of summer where the symptoms returned, along with an angry growl. So this spring I bought a new transmission.
I have no connection to CPN other than someone on this site recommending them, and now I will too. The parts were shipped reasonably quick. Honda seems to be able to control MSR pricing, so shopping around should yield the same prices. My only advice would be to go over your parts list carefully and order snap rings and other small parts you may need at the same time.

Here is a link:https://www.cyclepartsnation.com/oemparts/a/hpe/505ce3edf870022d24bdbb7f/transmission-tda