1990 f250 5.0 dual tank , truck starts running bad , backfire & quits running alltogether after the gas tank gets below half way mark also seems to be more of a problem on an up hill grade . Have flushed out the tank , changed fuel filter . and the front tank pump doesnt work at all

Have a repair shop go for a ride with you, as you
explain the issues

Then have them diagnose & resolve

Stay away from the Genies in a bottle, they only take
your money

If you don't understand the product & don't test a thing,
don't think a can of anything - will do anything

Local library.

If it has a timing belt,that is your problem

The exhaust converter & all the oxygen
sensors will have to be replaced as they
fired from the heat of a timing or misfire
issue

Check fuel pressure also after you resolve

GAS GAGE IS EITHER A BAD SENDING UNIT OR "SLOSH MODULE" IF A FORD. HEAT ISSUE IS A VACUUM LOCK IN THE COOLING SYSTEM AND NOT ALLOWING THE AIR TO ESCAPE AND NO WATER TO CIRCULATE.CHECK FOR LEAKS ,THE THERMOSTAT,AND WATER PUMP FOR PROPER CIRCULATION

Give use any codes you may have

I have a 2004 LS I will check my diagnostic
manuals for you

V6 or V8 ?

There is a metal chamber that is in the fuel pick up line about 1/2 way up designed to take the pulsation out of the pump.If the o rings are bad or the pump has been changed (some mechanics take the pulsator out and replace it with fuel line but if they didn't use fuel injection line it will only last like a few months.)
Either way sounds like the tank has to come out.

NOT SURE ABOUT THE FLUID MAY BE WATER LEAKING BUT, I WOULD TRY TWO INEXPENSIVE THINGS FIRST.ONE IS CHOKE -N-THROLTLE BODY CLEANER AND A GAS TREATMENT.

If you just filled up you could have some bad gas.Hope this helps.Good luck.

You most likely have a bad fuel pickup or a bad changeover switch if its dual tanks. Also like I have said before, one of the most common reasons for any fuel issue with this year is the fuel and wire connections on top of the tank that lead to every major part of your fuel system. No one wants to drop the tank or reach up and disconnect the switch to check. So I get these trucks for close to nothing from people like you and run them forever, after I spend a day replacing the needed wiring or pickup. to remove anything you must drop the tank or take a chance of breaking something. If you are uncomfortable doing this. I may be able to give detailed instructions. [email protected]

on your last tune up you might have gotten some bad plugs i know they are new but sometimes they dont work straight out of the factory and your fuel guage connections are backwards