Hello out there can anyone help me!!!

I have a sapphire 4x4 cosworth (91) witch runs fine in till iam driving down the road and it starts judering and missing at 1400-1500rpm. i was told it was the phase sensor so i replaced the phase/crank/air temp/coolant temp sensors and thought i fixed it but it hasnt???? also if i put my foot down hard its gets to 6000 rpm and cuts out then back fires and misses till i turn the engine off and back on again. i think these two problems a relaited but not sure?

PLEASE HELP ANYONE!!!!!