1998 GMC Jimmy Checkk Engine Code

[hifigt]

I have a 1998 GMC Jimmy and have been getting some repetative check engine codes since August 21 (I own a code reader). The first encounter I got codes P0740 (Torque Converter Clutch Circuit Malfunction) and P1860 (Manufacturer Specific DTC). Vehicle acted like it could not downshift when first set of codes were received. After a few minutes vehicle returned to normal and shift just fine. Got the same codes on 8/22. Next encounter was 8/27 with the same set of codes. Then on 8/29 got the same codes but this time the instrument cluster seemed as though it lost power but vehicle kept running fine. Tried to turn off vehicle when in park but could not turn key far enough to remove. Turned on and off several times and then was able to shut off and remove key. On 9/4 got a couple new codes along with the same codes mentioned above. They were P0753 (Shift Solenoid A Circuit Electrical), P0758 (Shift Solenoid B Circuit Electrical), and P0758 (Shift Timing Solenoid Malfunction). Again vehicle seemed like it could not downshift. After a few minutes vehicle clicked back into normal mode and run and shifted fine. Since 9/4 I get sporadic check engine light with a mixture of the codes mentioned above every couple days. Vehicle seems to run fine but when light comes on it seems like it doesn't want to downshift properly. I'm an elecitrcal engineer and this seems to me like an electrical problem.

Any help from anyone out there with similar experiences would be greatly appreciated and with what to do to fix problem. I know with previous experience when you bring a vehicle in intermittent electrical problems it is sometimes hard for techs to diagnois right away. I have been logging each check engine light experience on paper with the codes received and how the vehicle reacted.

Brian

[GMMerlin]

Most likely cause of multible transmission electrical codes is a faulty ignition switch.
I have replaced many switches for that complaint.