Td4 running issues

04 TD4

Egr delete
Ron box 2a
K n n filter

At 50mph 2krpm on very light throttle, just enough to maintain speed I get a light stuttering/misfire.

MAF has been cleaned but has Ron box so endless it was dead it wouldn't make a difference.

All serviced etc drives great pulls like a train all the time always starts its juts at that speed load point I get that stuttering its only light.

I'm thinking the fuel pressure sensor but don't want to shell out for one if it's not that.

Any ideas?

Thanks in advance