3000 tdi timing

Hello to all. Hope someone can help . Have just had some work done on 110,1986 converted to 300 TDi. I have had a new timing belt fitted and the mechanic said it6 was a tooth out but it was running ok and started ok even without glow plug. After havimg new timing belt it seems very smooth on the respones side but hits a brick wall at 55 mph as before would get to 70moh at a sencibel rate. I have noengine management fitted thought i would mention that. Has enyonr got any idias.Thanks debnrob