transmission problem

I have a Auto VX S Pack that has done 420,000ks, recently when going up hill or when releasing the accelerator to slow down for a corner or a car turning and putting my foot back on the pedal it creates a similar sound and vibration that the lines on the highway create when you start veering...

G'day all. posting on behalf of a good mate, great with cars but no so great with PC. The car is not exactly a Comodore, hope you fellows can help. 4L60 Transm. - V6 GM (VP 92?) combo fitted to Toyota Hilux, not long bought. The problem is when going down hill locked in low gear (creeping)...