1998 Ram1500 Laramie 4x4. With a 96 transmission not sure which one. troubleshooting when I bought the truck the speedo didn't work and shifting from 2 nd to 3 Rd was slippery. I finally figured out to change the abs speed sensor which helped a lot especially having abs after 6 months! Almost head butted the wheel. When I did the filter and fluid the first time it was black sludge to where I'm surprised it shifted at all. The second time about a month ago I changed the governor pressure sensor solenoid and the transducer. Which helped a bit. A little more grab but still slipping past gears when I'm giving it gas to go a little. Also changed the trans speed sensor and it still is slipping past gears into neutral until I let off. When I take off if on a hill it drags into going which is dangerous. But cruising along it shifts through gears like butter can't hardly feel a thing. It seems to still be limping until it catches up. In the beginning though the truck on take off would shudder something fierce so if that happens these sensors fixed that mostly and left the slip. Sometimes at the right throttle it takes off in first like it should with a little punch but not often.

 

Given the state of the fluid on the first change, I wouldn't be at all surprised if the trans didn't need rebuilt....

 

If it's in limp mode and you changed the sensors, time to look at rebuilding it like HeyYou stated. If it's shuddering, the frictions and steels are most likely burnt, or one of the valves in the valve body is sticking.