Shifting issues

I have a 90 GMC 1500 4x4. I was driving it and the transmission started slipping. I got it home and during the drive it was shifting really hard. RPM's would get pretty high before it would finally shift. I put transmission fluid in it when I noticed it slipping and limped her home.

There is a transmission fluid puddle under the driver's door where the differential is located. I'm thinking the differential seals are no good.

About a year ago my driveshaft came loose (yolk broke) and apparently transmission fluid poured out of the differential. I replaced the yolk, and put the drive shaft back together and added transmission fluid and had it back on the road.

Now, I'm thinking the differential seals are bad. When I start the truck and put it in gear it goes right in. While it's sitting. Drive, reverse, both click right in and I can feel the truck wanting to move. It's the going from 1st to 2nd, 2nd to 3rd etc that's bad. Is the differential bad or does it just need the seals replaced?

Ok, so I found the leak. It was one of the transmission cooling lines. It's been replaced. Fluid levels are good but it's still shifting at high RPM's. I'm wondering if it's a bad governor or something else.

Is there a TV cable on your trans? You might try adjusting that since it interacts with the governor to control line pressure/shift points.

Is there a TV cable on your trans? You might try adjusting that since it interacts with the governor to control line pressure/shift points.
I will do that either tomorrow after work or hopefully by this weekend. Thanks!