I have a question on this. Is there a good way to test/troubleshoot the senders?

Mine has always read high. So I bent the float arm a little to try to adjust it, but didn't see much improvement. Is there a way to test it to see if it's bad? (I have a '64 GMC 1500)

There is one place that you have not looked, and it is there - only there - that you shall find the master.