1988 Ford E-Series Van Code 41 "always lean"

I have a 1988 Econoline motorhome, 351W C6 trans, every once in awhile, I get a code 41 engine light, it comes on and if I pull over right away and restart, the light stays off until it happens again, usually after driving at highway speeds and then slowing down. It has a new selector valve, o2 sensor, egr valve and sensor, new spark plugs, wires, cap and rotor. It never happens with the koer test, it only shows up in memory. Also, it never affects the way the van runs. Very annoying.