ok lets try this:
put the + jumper Cable on the heavy wire out of the sol. that goes to the starter, it should spin it just like it did when you put the + jumper cable on the heavy lug on the starter.
This test is checking the connections on the sol, and the connection on the starter as well as the heavy connecting wire.

Yes if it jumper the two heavy lugs on the solenoid, the starter spins. Is that what you meant George? This solenoid bolts directly onto the starter so there is no heavy wire from the solenoid to the starter.

Ok, didn't know sol was on the starter.
Use a wire or screwdriver to jump the heavy wire from battery on the sol. to the small start terminal on the sol. it should spin the starter.
This will assure the new sol is good.

Ok if I jumper the hot lug to the start pin on the solenoid, it only intermittently spins the starter. Most times it's just a thunk. If I jumper the hot lug to the starter lug, the starter spins every time without fail.

This happened with both the old and new solenoids.

This part of the test....is the blue wire still attached while you doing that? If so, disconnect that blue wire and try jumpering without it and see what happens.

Yes blue wire is disconnected. I also tried with a wire straight from battery to the start pin, same result.

ok now we are getting somewhere, it could be the new sol is bad but it could be the big wire ends are not clean to pass enough current through the sol terminals but easily passes current when jumped by touching the wire lugs but no able through the terminal bolts.
do some inspection there.

Ok I took the nuts off both lugs on the solenoid and guess what I found? The little braided bare wire that feeds power to the starter is in bad shape. It literally fell apart. I tried to rewrap it best I could and put it back together, but now I get no spin on the starter at all when I jumper the two lugs together (but it does spark!).

I'm guessing there is no way to fix this, aside from buying a new starter? It seems it be made into it and no long enough to splice a new wire...

Whelp guys, that was it! New starter = crank every time!

Thanks for all the help!