Is my transmission starting to fail?

Just received a 1995 Pontiac Trans Port; 3.1L V6 from a family member with 175k miles. This vehicle has transmission problems I don't understand. First, reverse doesn't work under power at all. You can shift into reverse and nothing, just slips. Plus the car will be running fine for a while then after a normal stop the vehicle will stall. It feels like the car wants to start off in 3rd gear instead of 1st. After restarting the car, I can shift 1st - 3rd manually and that might work. When the car acts like this it feels like it is struggling to move forward and makes a weird noise but idles just fine. I can let the vehicle sit for a few hours to cool off and it seems to run fine for a while then back to the problem. I have checked the transmission fluid and it seems to be at a normal op level. As you can tell, I am not a mechanic just someone who's trying to get an idea of what I could be dealing with on this transmission and how bad it could really be. Thank you for your time and patients.