A hypothesis please!

[BADSAM]

I traded/purchased for a suburban about 6 weeks ago. It's story (they all have a story) was that it was a daily driver before the guy blew the bottom end of the engine. So I had an engine rebuilt for it, installed it and took it out for it's maiden voyage on Monday. I did a short trip (3 mi) around the neighborhood and it performed flawlessly. So I took it down to the gas station (4 more miles) and filled it up. On the way I felt a slight hesitation. After getting gas (I filled up) I decided to push it a little and headed out for a little longer drive, I went about 5 miles and turned around, on the way back the hesittaion came back and this time with a vengence. I had problems getting home, it was surging going up a hill, hesitating , etc. It felt like a clogged fuel filter. But I did make it home.

Sure enough after investigation the next day, I found crap in the fuel filter, flakes and what appears to be rust particles. I also tested the fuel pump and it's fantastic.

I cleaned the filter out and then took it for a shorter trip, even went down and up that big hill again. No problems. Although there was more crap in the filter by the time I got home.

So I figure the PO told me a tall tale about it being a daily driver and I pulled the tank today. To my surprise the sending unit is relatively new, the sock is in great shape. I could find no tears or rips in it, still very pliable. Looks NEW, as does the rest of the sending unit.

The tank is not corroded or rusty. It looks very good. There are a few flakes of ??? at the bottom of it. But it's not from the tank corroding.

So where is the crap in my fuel filter coming from?

My guess is:

1. Before sending unit was replaced there was no sock and debris collected in gas line, I had the good fortune during my cam break in to break all that crap loose in the line. Or rubber lines are deteriorating (but it looks like rust flakes?).

OR

2. Aliens put it there.

My plan is to go ahead and clean the tank out, blow all the lines clear with my air compressor, and replace all the rubber lines.

What's your hypothesis?

Thanks