llMoveToTarget() falls short of the target pos

I am having trouble moving objects to the desired position using llMoveToTarget.

I have a main object that rezzes several objects. The rezzed objects then move forward to a certain position. The problem is that the objects stop short of the target position and hence the at_target event doesn't fire.

targetID = llTarget(newPos, 0.25);
llMoveToTarget(newPos, 20);

If I set the range in llTarget to 0.5 the at_target event fires though i need the range to be much less.

I used llApplyImpulse and llSetForce thinking that the objects don't have enough power to move ahead. But that didn't help either.
Also sometimes one or two of the rezzed objects decide not to move forward at all!

Does anyone know the reason ?

if the objects are massive in size they are most likely running out of energy. Use llGetEnergy() in a timer loop to see what the object's energy is at, if it dips below .001 when your problems occur then that is almost certainly the cause of your issues. There is no way that I know of to "Refuel" an object for energy.