Ferm painted you the best case scenario there F&C. If the linkage and the shift cables check out within specifications then your next move is the clutch dog (attached to the prop shaft in the lower unit) which engages the forward and reverse ring gears. It can get worn to the point that it will do exactly what you described. It takes a ton of use in and out of gear to wear one out but the clunking you hear every time you move from neutral into gear is the clutch dog engaging the ring gear. The jumping in reverse with power applied is the clutch dog slipping from one cog to the next cog. Find the problem sooner or it will cost you a bunch later. I hope it is simply an adjustment. It wasn't for me.
