Could be many things.

As a first step, I would measure fuel pressure at the rail at idle and while driving.
Needs to be close to 50 psi steady.

As a second, I would do a proper smoke test (not a fluid pump/cigar job) with good smoke and pressure for 10 minutes..

The flammable brake cleaner test for leaks won’t work as the DME will adjust before you hear a difference.