2001 FLD starting issues.

When you key ON before you push starter button, does the truck go thru the normal start up procedure? The dash lights cycle? With associated normal noises.

Disconnect the power cable at the ECM port. Disconnect the whole plug end, not the single wire.
Replace fuse to see if it blows again. If it does you have a problem with the wire or connector, If it doesn't your problem is in the ECM.
My truck has 2 small fused wires that feed the ECM from battery. I don't know why this would prevent the starter from cranking.
When my ECM went bad the starter would still crank. Motor would not start. I don't think the starter needs the ECM to crank

 

The one time I blew the fuse, was because of a bad connection at the batteries. I was jump starting it, and had some smoke. It will crank, without dash lights, when blown. Something somewhere is shorting out. Could be a shorted battery. Maybe a wire got put in the wrong position when starter was changed. All I know is to inspect the hot wires for bad connections or corrosion. Especially the hots in the battery box, first the small fused line. There’s a wire from the alternator to the starter. Also a jumper wire on the starter, easy to get them crossed up. I wonder if the new starter could be the problem. Common sense says, something got shorted or went wrong when it was changed. But maybe not, since it didn’t happen right away. Somethings shorting the fused wire, good thing it’s fused, or the ecm would be ruined.