Installed a rebuilt 4l60e in my 94 z28, trans shifts fine but occasionally I get a service engine light to come on and the shift points immediately rise to around 3000 rpm during normal in town driving for 2nd to 3rd and to 4th. At WOT car shifts shifts fine. I cannot get any codes out of the ECM also. I don't have a scanner but when I jump the pins to retrieve codes I am unable to get into the service mode. No Flashing code 12 etc.Prior to the service engine indicators the shift point are approx 1800-2000rpm during normal in town driving.
Any Ideas from you pros?

Thanks in advance

Larry

 

Since you cannot retreive the codes flashing you will have to take it some where to get the codes read It will be worth it because you will get your answer to whats wrong instead of guessing most any repair shop should be able to read the codes for you