Bad computer? - '89 2.8 TBI

I have an '89 S10 Blazer 4x4 that has been having acceleration/power issues and a problem with excess fuel consuption for the last couple of months. I have either tested or replaced just about every sensor on this thing, checked fuel pressure and volume from the pump, pulled the catalytic converter to make sure it wasn't cloged, etc. The problem is getting progressively worse and I have never had any codes from the computer. I am getting a symptom I had not noticed before. In field service mode, it is not entering closed loop mode. Through process of elimination it appears the computer may be bad. Has anyone experience this type of problem before or is there a way to test the computer itself?

im not entirely sure if all stores have the machine, but i know that a few autozones have the ability to test OBD 1 stuff...