1993 Pontiac Bonneville Shifting Issue.

I have a 1993 Pontiac Bonneville. There is an issue with the shifting that I can't seem to figure out. It will shift into first and second gear every time. When it goes into second, a lot of the time, it will make the whole car jerk a little. Occasionally the car will shift into the higher gears (3rd and 4th). I've had some luck when I pull the car to the side of the road (when it doesn't shift past 2nd), turning the car off for a few seconds, and then turning it on. Then it will go into the higher gears (most of the time). I've tried just pulling the car to the side of the road, parking it, but leaving the engine on and then leaving, but it never works--only when I turn the car off, and then back on, will it temporarily function (around 80% of the time). For it to get into 3rd gear (when it does shift, on occasion), the rpms need to be around 3,000 and the speed approximately 50 miles an hour. When I get it working it stays functional for around 5-10 miles until it stops and then it drops down the 2nd and stops upshifting completely. When it doesn't work the rpms are around 3,500 at 55-60 mph (in 2nd gear). Also, I've noticed that when it's in 4th gear, the acceleration is strange. I will be at around 53-56 mph (and approximately 1,700 rpms) and I can push the gas peddle down, and it doesn't do anything to the rpms or speed until I push it down a substantial amount, then the rpms instantly jump up around 600-1,000 higher and then the speed increases. I appreciate any responses or suggestions. Thank you for your time.

*note*
The fluid was very bad when I first got the car, so I had the fluid and filter changed. After a few months the fluid was very dark again, but didn't have a burnt smell, so I changed the fluid and filter again to see if that would resolve the shifting issues. I also used some Seafoam Trans Tune--put 1 can into it before--drained some fluid to keep the level correct--and put in half a can after the last changing.