I have a 1988 gmc Sierra 305 th700r4 4x4 1500. When I shift to drive from park or reverse it slams hard enough to jolt the truck and spin the tires when on dirt. Then going down the road it will turn up to about 4500rpm before shifting. Did it a day or two ago. I jolt the kick down cable and it went back to normal. Now it's doing it again. Please help. Just changed out tranny last Labor Day.