So my truck just started doing this weird thing, I'll have OD off going down the road at 40mph and that sets my engine at just over 1500 rpms. If I start to go up a hill I have to give a little more gas and then the truck starts surging forward until I let back off the throttle. Sometimes the surging is coupled with a loud cough like sound from under the hood.

Any ideas?

 

Test the throttle position sensor. If that's ok, how's the plenum??

 

How do I test the throttle position sensor?

 

Multi-meter. Preferably analog. (with the needle that sweeps a gauge) Stick the black lead on the battery negative terminal, red lead goes to middle wire on the connector at the TPS (with it plugged into the TPS) Set the range on 10 volts. At idle, voltage should be less than 1, at wide open throttle, it should be greater than 3.5. It should progress smoothly as you open the throttle. If any one of those isn't as it should be, replace the TPS.

Digital meters aren't good for this test, they don't react fast enough.

 

TPS is fine, gonna check the plenum here in a little bit, though I'm pretty sure its probably blown.
One thing I noticed was yesterday was hot, like 90 degrees. The truck behaved poorly, all the symptoms I listed were amplified. But today its 40 degrees cooler and the truck is doing good. Not even close to how it was being yesterday.
I realize my engine is getting more air today but why would that affect it that dramatically?




Also, something I forgot to mention initially is the truck jerks randomly at idle.

 

You have a miss. Probably related to the blown plenum. How do your spark plugs look?