1987 convert,4+3 tranny.
If I drive at 60mph(1900rpm) or less  everything is perfect.I can drive all day long without problems or indications. Gas mileage excellent at 28mpg+ average. If I drive 65-70 (2000-2100RPM) within 20 miles I get a Code 32 sys light. Turn off engine then on and code 32 within 20 miles. Faster speeds turn on light in shorter distance.
Changed EGR which was originally bad and all was ok for a while now worse than ever. Replaced almost all vacuum lines in engine.
None of above affect driveability in any way.
Suspect MAF which checks out or possible worn throttle body.
HELP!!!! I am ready to take light bulb out.

Gerry