Problem:
Normal engagements - soft shifts.
Testing:
- If it feels like low line pressure, disconnect vacuum line from modulator. Check for harsh engagements and harsh 1-2 shift. If your line pressure seems high, check the vacuum to the modulator.
- Tee a vacuum gauge in series with the modulator and check for normal manifold vacuum.
- Normal vacuum is 19 or better at an idle. When you flash the throttle, the gauge should immediately drop to zero and then return to 19 or better.
- If the vacuum does not drop and return instantly during throttle flash, there is a restriction, usually carbon build up at vacuum source or a soft vacuum hose that is collapsing. You should always replace the vacuum hose. The thick walled vacuum hose seems to stand up better to the heat and harsh conditions under the hood.
- If the line pressure didn't improve when disconnecting the vacuum line check modulator with a hand vacuum pump for proper operation and make sure that the modulator valve is free in the bore.
- If the modulator, valve and vacuum check out okay, suspect the pressure regulator valve in the valve body or a pressure loss inside the transmission.