Q: The rpm jumps up and down about 300 rpm when accelerator is constant. Only seems to happen when traveling between 40-50 mph

Hello, thank you for writing in. The truck may be having issues with air sensors, fuel pressure, or other electronic issues. I have have to replace the fuel module and the mass airflow on my 1998 S10 with 168,000 miles. Fuel pressure can be tested in several ways, and you may want to start there. You should also have the truck scanned for diagnostic codes at your local parts store or by a technician. Even without a check engine light, there may be codes that indicate a component is about to fail. If none of the above is to blame, look into your gas recirculation system. For more help with diagnostics, contact our service department to schedule an appointment.