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Discussion Starter #1
Title sort of says it all.
I just bought this truck yesterday, told it was all rebuilt, had no issues running and driving. Just ugly (bad shape) interior, some exterior ugliness, and had to be started with a flat head screw driver instead of a key.

Well, I'm an idiot who needed a truck badly and a vehicle and I got swindled/lied to.

On the way home I discovered it wouldn't make it above 40mph, then 30, then 25. It gets worse the longer I drive it. Died a few times. It seems to get slightly better if I turn it off and back on. It will die if I floor the gas when it gets this way (struggling to hit 20mph) but then starts right back up. It didn't act like a transmission issue, and it isn't. The truck had a few back fires (mild/rare) but it really is just a "loss of power" issue like its starved for gas/air/something.
It acted like it was starved for gas which is why I did all the work on the pump and fuel filter.

So I got home and today I changed out:
The fuel filter
The fuel pump (verified working, watched the full injector spraying gas and watched it suck gas all the way through the new filter and get sprayed in)
Spark Plugs
Spark Plug Wires
Air Filter
Oil Change

All brand new now and functional.

It idles fine and doesn't die at all after it warms up for a minute or so.

I checked for vacuum leaks as best I could by spraying starter fluid all over the vacuum hoses/etc under the hood and it never revved up so I don't think it's a vacuum leak.
There are also no signs of leaks/fluids on the engine, and no oil drips.

My suspicion is the exhaust system, but I honestly have no idea where to start/how to diagnose those/that.
It has no catalytic converter and the mufflers are glass packs.

I can't afford to not have a vehicle, and I really got screwed here. I can work my butt off to fix things, like I did today, but I need to know what to check/what you guys think it likely is.
If you think I should start a new thread outside this intro asking for help please let me know. I need to start figuring this out tomorrow morning/this weekend.
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