I found I had a bad ground to the starter, ended up running new cables to the frame, then from the frame right to the starter itself.

Using a pair of jumper cables, I ran one cable from the case of the starter to the battery ground. With the key on and being ready for it to start, I connected the other jumper cable lead from battery hot FIRST then reached under the truck and connected the other end directly to the starter power stub. Be prepared for it to spark AND for the starter to spin up starting the truck. Pull the power jumper cable off of the starter power stub to disengage the starter. First, you want the spark as far away from the battery as possible. Second, keep all body parts away from stuff that will move and make sure the truck itself won't move after it starts up. I don't recommend this for the faint of heart.

This bypasses both solenoid and cable problems, so you'll still have to diagnose which one is the real problem.

On the old truck the ignition switch wore out so I had a special screwdriver to short the power line to the solenoid stub in order to start the thing. I impressed the heck out of an old geezer that some young schlub knew how to start his truck with a screwdriver. I moved on to hanging one of those remote starter switches out the front of the truck. This way I could turn on the ignition, then walk around to the front and squeeze the remote starter to get the thing running without opening the hood. I eventually fixed the switch.

You may notice a common thread of "turn the ignition switch on first." This step is fairly important.

Now that I've written this all up, I recommend you don't do any of it, LOL! Posted here for search purposes.

Diagnosing this problem is one of the advantages of having the solenoid up where you have easy access to it instead of next to the starter buried under the truck like other manufacturers.