147 jtd 8v running problem help please

[123quackers]

Have a running issue,seems to be in 4th or 5th from 2000 to 3000rpm only.. Feels like injectors sticking and holding back which causes lots of smoke.. If you pull away in first and go up through gears no problem its as if when you back off then go back on the throttle between 2 n 3ooo rpm it has the issue.. Any ideas?

Have thought bad fuel and put some injector cleaner in to try... But feel its a sensor not sure. Thanks