mitsubishi triton

i have a 2003 v6 triton(mitsubishi) it starts and idles ok but when u put the foot down it backfires and also when u try to drive it but when u just sit there and accelerate slowly nothing it only does it when u plant the foot and try and drive it
new head gaskets and new leads not new plugs but timing is 8% tdc all correct left hand side plugs are black and right hand side ones look like they are firing HELP