trans problem

[scottsales]

1997 ck truck 305 4x4 automatic. truck would shift perfect. yesterday went to drive and if takes off in high gear. it will shift using a snap on scanner and take off in low fine if you command low on the scanner to trans is mechanically fine I think. any help

[Jeremy-WI]

anything else happen at this time? Tach, speedo, or prndl all work. It could be a sign that your ignition switch is going bad

[scottsales]

tach speedo prndl all work have already replaced ignition harness.