Problems With 200tdi Conversion In My 90

when the conversion was finished everything was fine apart from when i get to the top end of the gears i find that thereis a flat spot like the engine wants to give more but u cant go any quicker the top speed is 65mph flat out i have tried some sugestions like advanve/ retard the pump timing changeall intercooler hoses for solid ones etc

is there any one out there who can give me any advice as iam stumped with this one

cheers

1. get a rev counter to check revs against speed,

2. If revs are hi change transfer box for disoc 1:222