P2626, P2237, P0171, P2237, P0172

Question

When Im driving between 10 and 30 mph the car will stop excelling and i have to down stop the car and start in 1St or sometimes even turn off and restart the car. Sometimes if I floor the gas when I feel the engine lag and let it get to 4 rpm it will catch up and keep driving. Where do I start? I don't want to put a lot of money in part replacements that are not needed. Thank you!