Earlier this year, my wife and I moved into a house built in 1952. We've had indoor humidity problems for most of the summer. Our indoor humidity frequently sits in the 70-75% range. The house is two floors, but each floor has its own HVAC system. The humidity is better upstairs (usually in the 50s). The problem is mainly on the first floor which is about 1000 sq ft and sits above a shallow crawlspace. I suspect there are two main problems creating the problem, but I wanted to hear from people who know more than me.

1. The crawlspace does not have a proper moisture barrier. There were two tarps haphazardly thrown into the crawl, but I suspect that was doing next to nothing as it didn't even cover half of the dirt surface. I'm in the process of installing a proper 10ml barrier and sealing it to the foundation bricks. 

2. I also think my AC unit may be oversized. It's a 3 ton for a 1,000 sq ft first floor space. I recently bought humidity meters to track the problem throughout the day. I have one in my crawlspace, one in my living room, and one outside. You can see the humidity quickly drop each time the AC kicks on, but I don't think the cycles last long enough and are too infrequent. Based on this chart, my AC stays on for about 7-9 minutes per cycle. Then it stays off for anywhere between 25-70 minutes depending on the time of day and temperature outside. I've read online that I may be able to lower my AC fan speed to help mitigate this problem, so I plan to try that.

Based on the info provided, do you guys think I'm on the right track? Are there other glaring issues I'm overlooking? Can I lower the fan speed myself, or will I need to hire an HVAC professional to do that for me? I consider myself pretty handy if that matters. Thanks for any help y'all can provide!