replaced starter and tested battery

 

Have you tried the plug still in but plug lead off test? This tells you if the ignition timing is causing the problem. Unlikely as, if the flywheel is out, it is usually well out and yes, I know you would have removed it to fit the new clutch. It is just possible for a new starter to be bad, I have had a few where internal bad connections have led to a "lazy starter". My guess is something you think you have fixed, or tested to be OK, isn't.