They did a load test on the battery I have to asume. That can still be flawed on occassion as the person doing it may not be up to speed. Temporarily subbing in another battery is about the only way to be certain. If it was accurate and good.

You may have a poor connection somewhere in the starter circuit as well or a poor starter. I would remove and agressivly clean all the connections that convey power to the starter.This incudes the relavent grounds in that sub system.

I always coat the connections with some form of dialectric grease before assembling to eliminate having to go back at them sometime in the future. This by the way is just general maintenance on older cars.

There is a short cut though. Using a booster cable from the negative terminal to a good ground point on the block and seeing if the starter turns over better. Reading the voltage drop from the centre of the positive battery post to the starter post under the starter load is another. The voltage drop observed should not be too much.