yes it is, what is happening is called engine braking. its to keep your pathy mfrom gaining unwanted spped going down a hill. what its going is shitting into a lower gear so when its going at the top speed for the gear the RPM'S go up so it slows down. nothing to be afraid of. it like if your driving and put your pathy in 2nd(if u have auto) its going to rev up to get the vehicle into thats gear speeds range.