I have no idea what is going on with my automatic transmission. When I start on cold car I have no problem with transmission. After 20-30 miles if I drive on slope and no pushing a gas pedal transmission go like to neutral. After that RPM=250. When I push gas pedal transmission not shifting. After that start shifting-neutral-shifting. I have no experience with automatic tranny. Is it tranny problem or/and some sensor problem. Excuse my English. I use dictionary to compose that help appeal. Thank you in advance.