[Three Peaks]

First things first.
Make sure all your connections are extremely clean and no corrosion, then retighten very well. Also, make sure you have a good ground to the engine and the starter. If you can, run a good ground wire from the battery to the starter.
The biggest cause of starter problems is corrosion or other interference with a good connection at the starter and/or solenoid, and an insufficient ground. Once you have that absolutely determined to be good, then look at starter problems since it looks like your battery is good.

Bob