My Tach is bouncing around and I dont think that it is reading correctly anyway. This the sequence of events....My harmonic balancer broke and rather than trying to fix a bunch of other crap going wrong on the engine I bought a used engine from the salvage yard....put that in and then like a couple of months later the trans went too. NICE !!! Well my car doesnt seem to shift at the correct times. I was told that the trans computer may have a problem.....After all of that the tach started its craziness. I thought had to do with me changing my GXE gauges to SE gauges. Give me a clue what I need to do or check.