"Service Engine Soon" transmission codes

[chevybill1]

1996 Chevrolet C1500 185,000 miles
Engine: 5.7L V8 SFI VORTECOHV
Transmission: 4L60E Turbo Hydramatic

I am consistently getting "Service Engine Soon" codes that seem to be transmission related:

P0753
P0758
P1864
P1860
P1886

At the same time the codes appear both tachometer and speedometer drop to zero and the shift inicator light (showing which gear is selected) goes off. The vehicle drives just fine, but does not seem to feel that it is shifting through the gears properly. In other words, there seems to be a lack of shifting. This is intermittent but very persistent.
A local transmission repair shop thinks that because there are so many different codes that the problem is probably electrical and very difficult to trace because it is not constant.

Any ideas?

Thank you very much.
...Bill