Transmission Control Module

I have a 1995 Isuzu Rodeo that is having problems, hopefully there is someone here that can help.

When this Rodeo was bought used, I had trouble with gears third and forth would not go into them, I had the transmission drained and new put in also with filter, checked all wires everything is good, the alternator is putting out 14.2 volts, still not shifting, checked harness and cleaned mode. still nothing,
now the box transmission control module under the passengers sit, as far as I know works, but if I unplug it it still does the same thing, has reverse and first, second. nothing else happens, is this a sign that this control module is bad.vechilie has 187,000 miles.
Is there anyone that knows about this??????

I'm not sure why you're not suspecting the transmission itself. You probably have some clutch packs that are wasted.

I have forgotten to say that this is a automatic and has been put onto a computer and no codes what so ever has come up. The company that check the Isuzu has stated it is electrical, and as I said I have went through the whole system, and the ideal was the control module. I am just asking advice if this could cause the problem or could it be something else. I just figured that if you unplug the transmission control module and if it does not change anything that I was doing then that could be the problem, any other ideals.....

I just had a transmission repaired that had the exact same problem as yours. It was out of a 97 Blazer but I'm pretty sure that the Rodeo uses the same basic transmission. The fix was replacing the 3-4 clutch pack. This requires removing the transmission and taking it apart.