Driving down road just stalled all lights were on.Tried to start and just turns over. changed coil and wires that work on my old motor.

lights come on, seatbelt activates but does not click or turn over. If I jump start it or roll it and pop start it, starts right up and I can shut it off and start right back up but then maybe the next day or 3 or 4 days later will not start. Always started fine but had the head gasket replaced due to massive oil leak, could oil have damaged the starter?

After started, check engine light comes on and idles very low. Hum is heard. Diagnostic code 46 comes up under transmission codes. Shifts hard in reverse at times. Feels like its stuck in higher gear but it cycles through all gears normally. Replaced park/neutral switch and transmission valve body but problem still occurs. Big decline in gas mileage. Any suggestions/ideas?