As mentioned earlier, try saddling up ( in - plane ) with your opponent, if you are coming in with alt and are carrying a bit of speed you may want to use lag pursuit as you are turning in behind your opponent. As Ghosth mentioned sometimes best to turn in / under behind them and come up in their blind spot. I would recommend not to cut engines ever, throttling back maybe, but do not kill the engine. Also, in the P51 no more than 1 notch of flaps, and that is if you are below 275/250 IAS....if you are able to get 2 notches down, then you are to slow entering the fight to start with and will not have the acceleration one needs to escape an overshoot if you do overshoot.......
If you see your opponent start to do a break turn( hard turn ) you should either go up or break in the opposite direction and extend. Preferablly extend in a gradual climb also......
Also, fly the P51 series in the TA or offline or DA.push it to its limits. learn what it can do slow and fast......learn what it can do at high speed , practice riding the tunnel, practice quick instantaneous turns, practice sustained turns at different speeds, practice learning to fly without looking forward all the time ( using up view/back up view/forward up view while flying - learn to use your lift vector & rolling to acquire target and keep eye on target at all cost), .learn at what speeds are best for certian notches of flaps deployed.......
example ( do not use these it is a mere example only )
220/190 IAS use 1 notch
170/150 IAS use 2 notches
140/130 use 3 notches
120/100 use 4 notches........
note I really do not recommend getting slower than 190/ or at worst 170 in the P51D, although it can be flown even at sub 100 speeds in a knock down drag out knife fight.......
go to the trainers website and fill out a Training Request form
http://trainers.hitechcreations.com/ hope this helps ~Good Luck~