1994 Disco 1, 5 sp. manual transmission. Starter spins the engine just fine when cold, engine starts right up. When the engine is warm, starter is very sluggish, cranking slowly, but engine still fires right up. I am assuming this is probably a "draggy" starter that needs replaced? I have a brand new fresh, high amp battery.

 

Go down to your local auto parts store, have them run a load test on the battery/alternator and a drw test on the starter to see how many amps it is pulling.
Most likely a bad battery.

 

Well, I thought it was the battery, so I replaced the battery, and there is no change in the starter behavior. I did this before I posted my question.

 

Then go have a starter draw test done.