hilux surf is going slow on road

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sent my Hilux surf 1991 2.8 diesel to a mechanic as it was getting harder to start. this is what the mechanic did. Remove belts and covers, remove cambelt, idler and tensioner and water pump. Remove injector pump. Send injector pump away for rebuild. Refit injector pump. Fit new water pump and cambelt and idler and belt tensioner. refit all covers and fit new fan belts. Set injector pump timing and fit new fuel filter. bleed lines. charge batteries engine. bleed injectors. check and replace glow plugs. Turns over good

Any way we got it back turns over real good. But for some reason it is slow on road. We could easily get to a 100kph on the road before we sent it to the mechanic but is struggling to get to 60kph. The mechanic does not know why is has all of a sudden it is going slow on the road. Was wondering if anyone might know why and how we can fix it