Right, since the mechanic can't read instructions on how to fix this out of a service manual they might get lost and confused when intelligence and knowledge is needed. This is more of an engineering type of problem. Diagnostic technician/mechanic is what you need maybe. They find the actual problem first then fix the problem on the first attempt. They might charge more but that's better than wasting money and time several times. Run engine to operating temperature, turn off all accessories, -turn key to on but don't start position, turn key to off, turn key on but don't start position, turn key off, start truck, engage emergency brake, put truck in drive. You can tell usually if it's relearning. The idle will jump around and start getting back to normal which can take five or ten minutes it varies. After it has smoothed out and back to normal idle in the drive position you can shift through all the other positions also and let idle in each position including neutral and park for about the same amount of time. You need to clear all the trouble codes first though for it to work. That can be done manually also.