sometimes with new pumps and with ones being used the seal in the pump bypass sticks to the side wall
when this happens you can get the bounce you talk about
removing bypass nut and insert from body (this is the lump on the side with a screw in it) careful not to drop guts inside pump,
(for first timers this is best done with pump out of machine with the bypass facing downwards towards the bench)
remove the piston in the nut, clean and lubricate, make sure the piston slides cleanly. reinstall and adjust pressure by way of the screw.
with older units dirt and scale builds up on the oring causing it to stick. when this happens get a small piece of wet and dry sandpaper, roll in to tube shape insert in hole and slide it in and out numerous times until the surface is clean
gauge fluctuations can also be the problem of the gauge or scale restrictions in the copper tube leading from gauge to water line
remember gauges on the machines are only used as a guide, and in many cases are not accurate.
hope this helps
havent worked out how to insert picks yet