Possible transmission issue

I drive for Postmates and I went on a delivery around 3:00 this morning. My truck drove fine. It has been having a build up of an issue. The acceleration over the past few days has been getting slowly worse. But it drove fine this morning. Then when I went to drive it at 8:30 this morning it went into first and got to 30 MPH but wouldn't go hire and wouldn't shift. So I pulled over and turned it off and back on. And suddenly it will start but wont shift into gear. I did finally manage to get it to drive so I could get it back home. But it threatened to stall anytime I tried pushing it past 30 MPH. I checked all the fluids and all the fluids are normal every day. But I do also have an unexplained leak in my engine bay which I thought was power steering but my power steering fluid is full. It is dirty and I can't figure that out either. I have siphoned out as much as I could and put new fluid in and it got real dirty again fast.