Cold Start vs. Hot Start Issue

[JSeegs]

1993 GMC 1500 w/4.3 V6
Remanufactured, low mileage, engine and starter.
Battery good, alternator new.

When I go to start the truck and it is cold it fires right up and the starter sounds normal.

Often (but not always) When I go to start the truck when it has been running and is at temperature the starter sounds like it is is struggling. Almost like the battery is just about dead. It always kicks over and runs but doesn't sound right to me.

I'd swear it did the same thing with the old starter and engine as well?

Ideas????

Thanks