1994 Lexus LS 400 Fail emissions: High NO

Engine Mechanical problem
1994 Lexus LS 400 V8 Automatic 172000 miles

Fails emisions test on 25 test for high NO.
25 test
reading allow
HC 11 103
CO .03 .57
NO 1570 712

15 test
reading allow
HC 18 107
CO .02 .59
NO 178 786

All maintenance is up to date: spark plugs, filters, etc. New pre-cat O2 sensors and cats are 2 yrs old. Cleaned out egr passages with seafoam twice. Have tried a used egr valve but same results. No vacuum leaks. Car runs good and no cel. Only thing bad is a slight valve cover leak that I think drips onto exhaust manifold and causes burning, but that shouldnt affect NO. New egr valve? Why NO is low on 15 test and so high on 25 test?