Having some problems with my '77 F100 302.

I have an edelbrock 1406 carb, Performer 289 intake, stock from the fuel pump back.

Here's the problem:
I'm idling fine when the engine is cool or hasn't been run in 30 minutes or so. After running a few minutes, I get a rough idle and the engine nearly stalls when I put it into gear. I've checked vacuum and I'm getting a steady 17 psi, checked the float levels on the carb: good there, I've even re-torqued the intake to 30 lb-ft to make certain there are no vacuum leaks. Still getting a steady 17 psi.
Put an inline fuel pressure gauge and I'm getting about 5.5 to 6 psi until the rough idle occurs, then I'm at about 3 psi. Everything from the intake up has been checked and double checked with no change in behavior: starts and runs fine when cold, but runs like poo after a few minutes. I can cut it off and it will fire right back up, but when I put it in gear, stall...
Also, I've set and reset the timing the correct way: pull and plug vacuum advance, turn distributor to best idle and vacuum, tighten.

I have a glass view filter just before the inlet on the carb and I noticed tiny flecks of rust in it. I'm wondering if I have rust in the tank that is causing the rough idle after the pump has time to suck the trash from the bottom of the tank.

Does anyone have any tips that may help me find the problem? Any experience here with rusty fuel tanks causing similar symptoms?

All help is appreciated!

 

My first suggestion would be when it begins to idle rough then pull the mixture screws and blow the holes out with air. Problem is plugged idle mixture doesn't explain the drop in line pressure.
Stuck floats might though. Is there any possibility that the rust is getting by the filter?
Is the fuel pressure gauge before or after the filter?
When it is acting up, how does it run off idle?

 

Wonder if the sock in the tank is plugged up?

 

Got an Update. This may help others who may experience similar problems:

Pulled the fuel line from the tank to the fuel pump off at the pump. Attached a 3' piece of fuel hose to the "in" on the pump, put the other end in a clean gas can.

Fired the mighty 302 up.

Ran great cold, let 'er run for a few more minutes with a noticeably better throttle response and idle. Put it in gear, and the idle dropped from 1200 to about 800 RPM. Better than before. Still a little rough, but I don't think I have the carb dialed in properly either. Definitely not what I was experiencing on Sunday.

Cut the truck off, remove the siphon hose from the pump, reattach the fuel line from the tank:

Runs good for a few minutes, but definitely a rougher idle, put it in gear, idle drops from 1200 to about 600. Doesn't stall, but does run rougher than when I was pulling from the gas can.

Based on this I'm definitely in need of either a gas tank, sending unit, fuel lines, in-line filter (I believe there is one on the frame, I have a new one by the carb), or all of the above. The only other way to isolate the tank would be to do the same exercise between the inline filter and the tank.

Based on another problem I'm having, I'm inclined to believe the tank is the culprit. Read below.


Another problem I've experienced is that gas seems to be evaporating from the tank. I bought a new locking gas cap, and it didn't help the problem. (figured maybe theft or the old cap wasn't sealing) The truck has sat in the same spot in my concrete driveway for 3 weeks now and I've gone from 90% on my fuel gauge to 25-30% I suppose I could either be losing gas due to a crack or hole in the tank (top because there are no signs of anything leaking under the truck) or rust has filled the sock up on the sender and is causing the float in the tank to sink. Not sure either way, and I won't be able to tell without pulling the tank. Either way, based on my little test yesterday, a new plastic tank may be in my future.

 

Quick Update:

Finally accumulated the funds and time to replace the fuel tank, fuel lines, in-line filter, fuel pump, in-line filter @ the carb, and took the carb apart, cleaned out the bowls, jets, air passages, metering rod holes, everything else. Put it back together yesterday evening. Runs like a champ! I set the warm idle to about 1200-1300 RPM, put it in gear, she drops to about 800-900. Right where it needs to be from what I've read.

You wouldn't believe the amount of rust inside the old metal tank. The original pick-up tube sock actually fell off in the tank when I tried to pull the sending unit out to inspect! I guess 36 years of service is enough. I hope I get 36 out of the new fuel system...

 

Thanks for the updates. Too often we never get to hear the proper diagnosis and solutions then we end up not learning anything.