2.8 tranny

While driving today the engine began to rev up and down. The best way I can describe this is it was a governor kicked in, but it was the tranny. Once I let of the gas for a bit it went away. But it came back and did it again, it was almost like it was going in and out of neutral.

I called a friend and we took it into a shop he works at and flushed the transmission fluid, which was BAD. I mean bad, it looked like oil and smelled like burnt up rear end gear oil. So we flushed it for awhile, but not until the fluid was perfect, he said to drive it like that for awhile b.c he's seen fluid that bad before and after a flush the transmission went out, then again he works at a Chrysler dealership and dodge trannys suck. We also changed the filter.

This helped and it seems to be shifting smoothly, but it did get it to do the weird rev thing again. I was thinking it could be a bad torque converter.... Anyone have any ideas?

What year is the truck?

1988 s10 4x4. drove it today to school, good 40 miles, and it shifted fine.