98 Legacy GT sending unit question

[SubaruPain]

Before this car/mechanic breaks me.......
I recently purchased a 1998 Legacy GT, the car ran fine but had transmission problems. The tranny was replaced and the car ran fine again for about a week, then it over heated (gage never showed hot). A warped head and $1,600 later, the car is running again but the water temp gage is still not registering. I'm now being told the gage is not working because the Engine Computer is bad. My thought is, if the computer were bad the gas/air mixture would suffer and the car would not run right. In any case, I thought I read somewhere that this car might have 2 water temp sending units. 1 for the computer and 1 for the gage. I am just looking for someone to confirm there is 1 or 2 temp sending units and if they have ever seen the computer make the water temp gage fail. I really want to get the gages or even an after market gage working so it obvious the next time it starts to overheat. I was in hopes this would be my sons first car, but we cannot seem to get it functioning well enough for me to trust the car on the road.