Driving a mk4 1.6 manual petrol 53 plate atm, 17,000, had a crash about a month back, some guy pulled out right infront of me on a main road! he crashed into the front left wing of the car...

Got the car back about 2 weeks ago from the garage, drove fine for the 1st week, but from a few days ago, i notice that if i redline it in 1st gear and shift to 2nd gear it doesn't jump anymore, it kind of slows down, feels more like my sisters 1.2 litre clio lol!

it also just feels a little sluggish overall, had no fault codes come up so i'm abit confused, this loss of power only comes in the shift from 1st to 2nd gear, not from 2nd to 3rd etc, and it's doing my head in!
Tyre pressures are also fine, I can't think of anythnig else that it could be?
Any help much appreciated
