1993 k1500 with 700r4. The truck needs to be at 35 mph in order to shift from 1-2. It needs to be at 55 to shift from 2-3. And I haven't had it fast enough to go from 3-overdrive. The fluid was dirty when I changed it and the filter. It is not low on fluid. I tried putting an additive, that was very thick, in it. It shifted normally for half a day and then it was back to high speeds shifting. Anybody have any ideas as to what is wrong?

It also drops into gear, from park, very hard. On occasion, it stalls out first thing in the morning, when I put it in reverse.

 

Change your fuel filter and see if it improves. GM transmissions are very cranky about this.

Allan