and more 4wd question

[viking64]

finally got to take my SVX out on the highway for a drive and just have a querry. I was travelling at 115kph, @2500rpm with cruise control engaged and no problems at all except that after reaching (going up) a slight and main incline the moment the car was over the crest, leveling out or just beginning to go down you could feel 'a shunt' is the best was to describe it. At first I thought it was the cruise control but to increase and deacrease the speed was all good. The rpm stayed steady at all times, no hunting or changing of gears - but just seams like when the car goes to reduce power 'cause it is no longer climbing the hills something is thumping back or is there a power/load shift from the rear to the front?
Of note is that when the car goes from the bottom of a decline (cruise/low power) and starts to climb it is flawless.
Any ideas or similar experiences?