Missing/pinging, 3.0 KS Verada

[KS95Dave]

Verada is missing badly -intermittently when under load (up hills). Runs fine when free revved or driven on the flat. If you put it in Drive and rev it with brakes on -i.e loaded - it misses and makes a loud metallic noise on the front bank as it misses, a bit bit like pinging from over-advance.
Revs fine in neutral.
Anyone got any ideas?
Driving be crazy.

KSD

[KS95Dave]

Took it to local mechanic who did a great job. Changed plugs and timed it. Runs like a bird. Now the central locking is doing its "dance" again. AAARGH!