'97 Sidekick Sport JLX 1.8l, 4-speed automatic transmission sometimes shifts hard from neutral to drive or reverse sitting at idle. It will go most of a day shifting smoothly then start hard shifting. Other days, it shifts hard from the start. It behaves as if the modulator is working intermittently. I understand that it is not a vacuum modulator on this transmission. Is there a way to test the modulator and where is it located?