trust me, your third finger is alrite... it's the 4th finger that's playing some tricks on you...
well, they share the same muscle, and the 4th finger is usually the weakest of all....
(unnatural, if not "weak")...
i remember how i overcame this barrier....
it's about the motion of your arm that carries through the scale....
watch out for the direction....
when you play (continuous from first to the 5th finger)
you hand arm should be moving upward away from the keys... like a "U" motion....
another way to practice is.....
only play note by note...
ie. suppose you wanna play g,f,e,d,c on the left hand....
put your 5 fingers on the keys (without pressing down obviously)
when you play g, only your thumb goes down the others remain stationary
and so on for every note, such that each note is clean...
that way you can get to have a feel of using the same amount of force by every finger
Topic: the third finger