My 2001 was external. The pumps were external up to 2004.5. There was a recall on them where an intank was retrofit. The green machine is external isn't it?

You can push through a pump. Not draw through it. His PSI is a bit low anyway. It should be around 10 PSI not 6. It sounds like Maaaayyyybeeee, the conversion was done and the original lift pump was left to be pushed through. You know how mechanics can be. In more ways than one too. Half a job. . . .

So I am thinking they are trying to suck through an intank pump under those conditions. It's an educated guess really, but worth a look.