I have 2003 307 automatic transmission but she has been give?

I have 2003 307 automatic transmission but she has been given me gear box fault and also when I start it jumps in gear 3 or 4 atimes, it becomes very heavy to accelerate also any time I come to to total stop it doesn't start with gear one as usual, I changed brain box and cleared all fault using computer now she's start with gear 1 but when i go slow on traffic or stop it will start with 3 gears I have chance gear oil.
It also show the --- sign instead of the D for drive R for reverse N natural I'm tired of spending money on this thinking of selling her out.