Kangarooing would normally be caused by some fuel/air issue e.g. a semi blocked fuel filter where at light loads (idle / reverse) things seem okay but at heavier loads not enough fuel can get through. Definitely worth double checking the fuelling and any compromised gaskets.
How severe is the kangarooing? It might be worth me recounting a problem I had many years ago after a service at a well known Lancia specialist. Leaving their premises and everything was fine but not long after there was this bad kangarooing which seemed to rectify itself before happening again. It turned out that one of the threads to a screw for the points had been damaged slightly. Because the points were then not seated properly it was causing some, um, interesting timing issues and the kangarooing.
