Sub dying on the highway

'02 Sub, 5.3 2WD 204k miles

While on trip from Mississippi to Manitoba we had problems with truck dying at highway speeds. Funny thing is it happened most of the times when my wife was driving. It was usually on a grade or passing, so I suspected the fuel filter. Tinkering under the hood on the shoulder I found the neg battery cable a bit loose. Worse time it happened was in busy traffic in KC. Stopped at a quick lube place and tried to get them to change the filter but the guy said it looked new and he didn't want to do it. (I changed it last summer on vacation when it acted the same way, no problems since then) He told me to go down the street to Advance Auto and let them hook it up to their diagnostic machine. When I got there all they had was code reader and it was showing no codes. I bought a filter and a few bargain tools to change it. Gas looked dirty running out of the inlet side of the filter. It ran fairly well the rest of the day and had no problems the next day. When we got to our destination I changed the filter. On the 1350 mile trip home it only hiccuped once (again when the wife was behind the wheel!). Shortly after the first problem I added Heet to the gas and started adding Lucas gas treatment at every fillup until I used up the quart.

Spark plugs have 120k and almost 5 years on them, I know they need changing.

Just had the intake pulled and the knock sensors and wiring changed to stop the knock codes last week before the trip.

I would check all your basics. Air filter being clogged, take the inlet snorkle off the throttle body and turned the butterfly and see if it has alot of carbon build up. Honestly, if you can get it to do it again I would put a fuel pressure gauge on it and watch the pressure.

My 01 K2500 4WD would die for no reason while driving. I'd wait a few minutes at the side of the road and it would start right up. I researched it here and found it to be a crankshaft position sensor. Dealer didn't believe me at first until they were able to record it in realtime when it died on them. Cheap fix (under $200) No other codes were stored apparently.

'02 Sub, 5.3 2WD 204k miles

While on trip from Mississippi to Manitoba we had problems with truck dying at highway speeds. Funny thing is it happened most of the times when my wife was driving. It was usually on a grade or passing, so I suspected the fuel filter. Tinkering under the hood on the shoulder I found the neg battery cable a bit loose. Worse time it happened was in busy traffic in KC. Stopped at a quick lube place and tried to get them to change the filter but the guy said it looked new and he didn't want to do it. (I changed it last summer on vacation when it acted the same way, no problems since then) He told me to go down the street to Advance Auto and let them hook it up to their diagnostic machine. When I got there all they had was code reader and it was showing no codes. I bought a filter and a few bargain tools to change it. Gas looked dirty running out of the inlet side of the filter. It ran fairly well the rest of the day and had no problems the next day. When we got to our destination I changed the filter. On the 1350 mile trip home it only hiccuped once (again when the wife was behind the wheel!). Shortly after the first problem I added Heet to the gas and started adding Lucas gas treatment at every fillup until I used up the quart.

Spark plugs have 120k and almost 5 years on them, I know they need changing.

Just had the intake pulled and the knock sensors and wiring changed to stop the knock codes last week before the trip.

Your plugs need replaced and with the up dated AC Delco plugs.
Bad plugs over work the secondary ign system and can cause many problems.

Fuel pressure should be tested when it acts up and also checked for lose of spark when acting up.
Any check engine lights on or flashing?
Codes should checked and code no posted back.

Thanks for the ideas. I will change the plugs, would like to also put a new fuel pump in her, but I know that is a job. I have been advised that 150k is about all you can expect out of the pump. When I changed the fuel filter it cranked up fine so the pump seems to be getting the gas to it.
Now that we are back home and just doing local driving it is working fine. No check engine light or codes.

Thanks for the ideas. I will change the plugs, would like to also put a new fuel pump in her, but I know that is a job. I have been advised that 150k is about all you can expect out of the pump. When I changed the fuel filter it cranked up fine so the pump seems to be getting the gas to it.
Now that we are back home and just doing local driving it is working fine. No check engine light or codes.

A lot of pump mileage depends on the care you good care you give it.

Run the complete duel pump pressure test to check out fuel pump.
And check out that fuel filter.