High speed miss-fire

[alanb]

My 1996 5.7 vortec tahoe drives great, but when driving at 65-70mph there is a slight miss-fire mainly on over run, I have changed all the leads plugs HT cap rotor etc, the MIL light has not come on.
I have checked the Camshaft retard with Scantool and it's running 12 deg with the RPM over 1000.
I don't want to mess around with the camshaft retard yet but could this cause the high speed miss ?
I was thinking it might be the EGR ?

 

[SunlitComet]

If you mean the alignment offset between the two sensors is 12 then yeahthat will do surprised you have not thrown a p1345 code yet but that just means it sees some other eligibility factor to pop that code is not being met. Typically it means it sees more then one issue. Reset your dizzy and see if that resolves your issue. At highway speeds with a consistent speed on flat land is when you timing will advance the most and most likely when the misfiring will occur.

---------- Post added at 11:28 AM ---------- Previous post was at 11:23 AM ----------

Your cel light still lights on startup right, not burned out?
BTW the egr valve has codes itself and with the right scanner can tell you its position actual and requested so you can look for anomalies there if needed. Don't know what kind you got tho.