runs great for about ten min, until it warms up

runs great until it warms up, then it shifts too soon. i have to turn overdrive off. rpms lowers a little. If I’m going slow like in crowded parking lot, trying to back out, it may die several times. it starts right back up and I can drive down highway without any problem except for having to turn off overdrive. But until motor warms up it runs great and I don’t have to turn overdrive off