Car seems to be not dynamic enough, accelerates poorly

The car is Opel Astra H (2006, 1.6L). I’m having problems with this as the symptoms don’t appear all the time so it’s hard for a mechanic to diagnose. Since i bought the car i had slight problems with the car accelerating poorly, especially on lower gears. Sometimes running the car from stop position on gear 1 resulted in worse acceleration than a bicycle. The car was shaking when driven very slowly (1st and R gears) when applying the clutch. I thought the clutch was slipping so i had it replaced and it’s much better now – the symptoms occur less often, but still there’s something wrong.

• The car is shaking sometimes when driving very slowly and applying the clutch (happens rarely)

• The car will accelerate extremely bad sometimes when moving from stop position in 1st gear (just like it would start from 2nd or 3rd gear) – (happens very rarely but can be dangerous)

• The car will jerk just a little bit when driving at normal speed and changing gear (after releasing the clutch) (happens quite often – doesn’t bother me all that much, but might be connected somehow)

• You can feel that sometimes the car is not accelerating properly or good enough especially in lower gear range (1-3). One mechanic told me while driving and checking it out that this car won’t do any better (it’s 105 HP), but i can feel it doing better sometimes (it’s 50/50 chance to get either experience).

What should i do, how can i diagnose properly? I had suggestions it might be the camshaft of crankshaft position sensor that might be involved here. Is there a way to diagnose without taking the engine apart?