I discovered this past week end that when in 4L and on the pedal a bit it jumps into 4H. If I hold it in 4l it stays and seems to function as it should. Awhile back I did have to pull a fairly large branch out of the linkage, not to sure if it bent anything and wouldn't know to look at it. If this isn't it what other causes and fixes should I be looking at?

Thanks,
Derek