Have a 2001 Ram 1500 - 2WD. Transmission was shifting hard into 3rd or 4th depending on how hard accelarating. Really noticeable if you kicked it down at highway speed when it shifted back up it would "hit". It was not really shifting down properly from overdrive at highway speed unless pushed hard on accelarator. Truck gradually speeds up but very sluggish and underpowered. I added a trani oil treatment about 500 miles back. Now it slips badly in 1st gear when coasting in traffic. Not always but often enough. This started 2 days ago. RPM's jump up to about 2600-2800 with only half the movement speed I should be getting. It still shifts hard in higher gears. The oil was clear, now it's very dark. Whats going on?