It depends on your mechanical ability. If you have a test light,a multi meter and some knowledge on how to use them, you can diagnose all of the external wiring for the e40d including testing the solenoid packs.
First things I would check would be fipl like mentioned already, almost every e40d truck that comes to me needs adjusting the fipl. Here is the test for that.
1. Wire A is reference voltage sent to the sensor from the computer ORANGE/WHITE
TEST: With the KEY ON, ENGINE OFF voltage should be approximately 5 volts.
2. Wire B is the ground path from the FIPL sensor to the computer BLACK/WHITE
TEST: With the KEY ON, ENGINE OFF voltage should be volts?? or less.
3. Wire C is the throttle opening signal sent to the computer from the FIPL sensor .
TEST With the KEY ON, ENGINE OFF and the throttle at idle position, voltage should be approximately 1.2 volts. With The throttle fully open, voltage should be approximately 4.5 volts. ORANGE/WHITE (CENTER WIRE)
The sweep from 1.2 volts at idle to approximately 4.5 volts at full throttle should be smooth. A meter with a snapshot or min/max capture mode is useful to catch intermittent "opens".
If the previously described range cannot be attained, FIPL adjustment can be achieved by rotating the sensor (on its bracket) one way or the other until the voltage values are satisfactory.
Next easy thing to check would be brake lights, and your brake light switch. If you have any bulbs burnt out, including your third brake light, your trans will act up because the e40d reads into the brake light circuit to know when to unlock the torque converter.
Last easy test would be to pull codes like mentioned. You can buy an obd1 scanner for $35 on eBay, or you can do the test manually, following this diagram and counting the flashes. There are many YouTube videos on how to perform this test.
You must be registered for see images attach
You must be registered for see images attach