Ford Ranger manual "down shift" feeling when cold

2007 Ford Ranger, 4wd, manual transmission.

The truck has a quick, intermittent “down shift” feeling when driving on cold days. The feeling could also be described as when you quickly take your foot off the gas and then put it back on. I have a 35 minute drive to work and it happens the whole way there. It also happens in 4wd.

Is the check engine light on?

Has it ever come on when this happened?

No and no.

So, are you saying that the engine cuts out very briefly and then recovers? Or, does the engine race without the truck speeding up? How many times a minute does this happen? Some of the important details that you left out are which engine do you have and how many miles on this truck?

You might borrow a scan tool and monitor the live data while someone else drives and you watch the IAC position, throttle position and RPMs. The throttle may be dragging on carbon in its bore when the pedal is released.

The engine feels like it cuts out very briefly and then recovers. There are about 50400 miles. 4 liter, V6, 5 speed manual.

It does it about 6-8 times in a 35 minute span. Sometimes real close together, other times further apart.

A Ford specific scan tool can run the engine on self test. That may pick up on what the problem is. You may have to go to a Ford dealer and pay the diagnostic fee. (Note that the better independents will be able to do this too.)
You might have better luck with your request for help here.