95 S10 4.3 Computer Questions

I have a 95 S10 (TBI) and i believe the computer is bad... the engine is not anywere near as powerful as it was.  It feels almost as if the engine isn't controlling the timing as it should.  the Computer is SN 16230703 Are there anyways to test this thing without taking it to the dealer?  When i put it on a OBDII Scan tool it says "cannont associate with ECM."  The check engine light is not on nor has it ever been even after 143K miles.   I did have to replace the Intake manifold gasket at about 120K. but i set the timing back right were it was at 0deg at idle as the decal under the hood said.

Part 2.  I will doing a fair bit of towing, and was wondering if i can put a mild cam in this engine and still use the stock computer and EFI setup.  (can the computer compensate enough)  I know my milage is going to go down, but I would prefer to keep EFI as this is my everyday driver. 

Make sure the wiring harness is in good shape and the connector is clean and everthing and we'll go from there.

That was the first thing i checked as well as all the fuses for the entire truck. none were bad.... Everything looks to be in Ok shape.