N14 cummins boost question

I'm working on a n14 cummins. In 8th-9th gear between 1600-1800 rpms it's losing boost for a second
then returns. Happens a few times then might be fine for the rest of the
day. Only happens under load. I have new injectors, ran the
rack, good fuel pressure (doesn't drop out when it looses boost), swapped out ECM, replaced map and speed sensor, air to air is fine, turbo is good, working on replacing the wire
harness-we'll see if that works. Looking for any ideas in case the wire harness doesn't work.
Thanks

 

Thanks for your responses. Forgot to mention that I already checked the tps and when the truck looses boost the tps doesn't fall out. As far as turbo lag, it builds boost nicely until it falls out, then comes right back. Checked it with the laptop and doesn't seem to have a problem building boost. This turbo doesn't have a WG. Any other ideas? Thanks.

 

It's an International Paystar 5000. I'm replacing the whole harness on the engine side right now. I repaired the #2 injector wiring harness because #2 injector was malfunctioning.