OK Ive had this fixed numerous times, can someone here please give me some insight into what the **** to do. I have a built trans, 3600 vig, with a trans cooler. Now ill be driving down the road and come to stop and it takes off in 3 gear, unless i manually pull it into 1st. Or sometimes whenever i go down the road my converter WILL NOT lock up and then once I come to a stop I get the same problem as stated above. The fluid is FINEE! It looks/smells brand new. Whenever It does this ive tried manully shifting it but it will literally SLAM into gear..jus BAMM there it goes. Anyways this only happens every once in awhile. IT could happen once a month, or twice a day, or only at 6:49 pm on tuesdays. Its just random as to whenever it wants to do it. The shop put a new valve body in it and new solenoids, but it still has problems. Help me. PLEASE.

 

Have you tried pulling codes? It sounds like it might be the dreaded PO757 or PO751 code issue with a higher stall converter. You need a tuning program so you can remove the error checking for those 2 codes. With a converter they will pop on at random and cause the issues you are describing above. No one really seems to know why, some peoples cars never do it, some do it once and a while. It doesn't matter brand of converter or stall speed, its very random.

 

What he said is correct Your problem is a tuning issue not a trans issue.

 

Trans was tuned whenever It was put in. Its been happening ever sense

 

Yes but many tuners for some reason neglect to remove the test for the code po757 and its a comon issue actually, Whats happening is this.
You PCM compares the MPH the car is running against the engine RPM , Well due to the stall converter the engine RPM is higher than the PCM expects to see on the 2-3 shift so the PCM thinks the 2-3 shift did not happen , So it sets a CODE PO757-SHIFT SOLENOID B STUCK. Then in turn sets max line and 3rd gear only.
Have the test for that code removed from tuning and you will be all good.
Someone post or calls me asking about this ussually a few times a week after installing a high stall converter.

 

I will give that a try. Thank you.

 

Your welcome