My 1998 gmc jimmy transmission is not shifting right. i just had the fluid changed it was black looking. after changing the fluid it shifted ok at first but now the fluid is starting to get dark looking again and it is not shifting right but it is not all the time can you help me

I would try changing the fluid and filter again. Sounds to me like there is a lot of crud built up in it and another change would probably do the trick. It probably wouldn't hurt to add a bottle of Lucas Trans Fluid at the same time. It will help extend the life of your transmission. Black fluid would likely be clutch material that wears off over time.
If this doesn't work you are likely in the market for another trans. Hope this helps.

It could be your bands slipping causing the oil to get a burnt black colour. I would suggest changing the oil again and getting the bands adjusted. The slipping of the bands could explain poor shifting. If the bands are worn from slipping, you may need expert support. Rgs Michael

My 1998 gmc jimmy 4wd wont shift in reverse