I have a newly rebuilt 700r4 which shifts smoothly through all gears but it doesn't perform it's first shift until almost 4000RPM. The trans was rebuilt by a professional who I have good faith in, he thinks that I need my differential ratio changed. Last year a different mechanic who I now don't have good faith in did change my ratio but I don't remember what it was changed to. Would this actually have an effect on the shift point or could it be a faulty TPS or some other cause? Throw me some ideas, this is a constant problem with this car, no matter what is done to it it will always shift late.