1996 Pontiac Sunfire 2.2l that trips the ETS off and check engine lights?

I have a 1996 pontiac sunfire 2.2l that trips the ETS off and check engine lights. When I get to 65-70mph, the car seems to down shift to a passing gear and trips the lights. Removing battery cables will clear the lights until, as previously mentioned above happens. Wondering if anyone knows what would be wrong, cause I don't want to be just throwing parts at the car to try and fix the problem.

Thanks, Brad