I got a new transmission for my Honda Accord exactly a year ago and it was working and shifting fine till the day I took my car to the mechanic for them to work on my injector mouth,I noticed immediately I left the mechanic my car transmission started shifting at 3rpm when normally it shifts to the next gear between 1.5rpm to 2rpm.please help as this is giving me a serious concern.

Always learn. U see the biggest mistake in Nigeria are mechanics. They can never get how factory did it. Sometimes u will feel you are over sharp,gbam they will do wrong connection. Best advice I will give u now,pls just buy direct tokunbor injector mouth,untampered,wires not mixed or cut and join by the so called nonsense rewires. If you doubt me,go to another mechanic and rewire,they will add their own then your gear won't select again. Better listen,it's cheaper to buy toks injector mouth than to visit different hands
They are all useless.

Lascode:
I got a new transmission for my Honda Accord exactly a year ago and it was working and shifting fine till the day I took my car to the mechanic for them to work on my injector mouth,I noticed immediately I left the mechanic my car transmission started shifting at 3rpm when normally it shifts to the next gear between 1.5rpm to 2rpm.please help as this is giving me a serious concern.

I would advise you continue to drive the car like that. Don't do anything yet. As far as it is not affecting your drivability

If there is a check engine on the dashboard please scan and share codes here