I have 2 yellow tops so I'm pretty sure the batteries are good. Starting is a little funky after sitting for a while. I checked to see if there was any drain on the battery while sitting and it was in the fraction of a milliamp range.
I just tossed on another 2GA ground wire from frame to engine too.
Passing thought from a past experience I had when I was rebuilding alternators:
Load test you batteries individually using a carbon pile tester to make sure one is not internally shorted and pulling the other down. I think Autozone can do this for you and in some cases I hear it's for free. I have encountered brand new batteries that have malfunctioned.
Definitely check the batteries, they can do some screwy things if one has a bad cell. If you are convinced its the starter, check on this: I was originally going to use a ford-cummins adapter for my conversion. This would require a stock dodge starter which I purchased new on e-bay at a substantial discount. Delays on the adapter caused me to go a different route on the adapter that used the starter from the donor van (GM). I kept the dodge starter because it appeared that I could swap the nose on the starters and maybe a new bushing in the nose and be good to go. Just a thought.
An often overlooked item is the battery cable. It can appear to be fine, but when you peel back a little of the insulation at battery terminal lug you may find some nasty green corrosion. It can get hidden because we like to keep everything wiped down and clean looking! A new cable is about the oonly sure cure.
I had trouble with a couple of cheap aftermarket ignition switches that were unable to pass enough juice to hold starter relay/solenoid and keep fuel solenoid open at the same time. I changed to a push button start switch and problem solved.