I flew the garrett on a couple of planes, the MU2 and the SW Metroliner
its been well over 26 years, so here goes on my fading memory.
During start, dwelling in a certain range is almost always caused by a BOWED SHAFT due to uneven heat dissapation during shut down
we use to pull the prop through a number of times after shutdown to avoid a bowed shaft for subsequent starts.
IF the engine would not accelerate through this range we gave up on the start and sometimes would go out and pull the prop through a number of times to get rid of the heat induced bowing.
but then again I could be wrong