Lazy pistons wouldnt give the above effect, good bit of tar and standard pads, or a grind and good trials specific pads e.g koxx bloxx, rock pads etc would give you back your brtake performance It could also be the cylinders moving in their moints, check theyre correctly tightened, and that the tthreads havent gone a brake booster , if youre not running one, would help stop braking power being wasted on frame flex....