Thank you both for your help, it turns out that it was the MAF in the end, which has been replaced and is running well

Hi all Desperate for some assistance My 2001 LPG Converted 4.0 HSE is giving me a big headache. When I start up the engine (on petrol) it runs like ****e...........especially when pulling away ,no power. Additionally once I reach about 3000 rpm the is no more power available above this and...