Occasional loss of power

I have a 07 Tacoma TRD sport 4.0 v6 auto double cab long bed 120k miles. Occasionally on the highway around 50-60mph I feel like I'm losing power and something is holding my truck back from accelerating, after a few seconds it goes away. Sometimes it doesn't happen at all. The only way I can describe it is like something his holding my truck back then all the sudden releasing me. My pedal is usually very responsive and when this problem happens I can give it more gas but it doesn't want to speed up it just stays around 50mph and about 2k revs. There is no clunk in the shifting and I do not have a rough idle and no check engine light. Any ideas? I been told possible tranny issues to maybe a bad coil.

 

Any codes? Even though the CEL isn't on..

I usually start by pulling up short/long fuel trims on a scan tool and going for a test drive. I'd be curious to see what they do when the power loss happens

 

No lights or anything. It's very odd it's not a violent event when it happens it just happens and the truck just struggles to stay above 50 like I'm going up a steep hill then it goes back to normal. I have not felt it driving around town or if it is happening it's not really noticeable because now every time I drive I'm over thinking everything. I had a brake issue before this where the truck would shake on the highway and my brakes would lock up. I made the mistake of throwing the parts cannon at it and basically replaced the booster, master cylinder, brake lines, calipers (front only), pads and rotors. I might try and record the event if it's safe enough usually at night I have a small section of highway to myself.

 

2,000 rpm at 50mph sounds like it is in 4th gear. Maybe the truck is trying to shift to 5th, but it can’t?

2,000 rpm in 5 (D) should be right around 70 mph. If I remember correctly in 4th gear, 50 mph it is about 2,000 rpm.

 

Merely a guess but could be an oxygen sensor. Don't test by replacing though..just that it sounds mirror image of an Oldsmobile I had back in the day, took a few weeks to get the CEL and that's what it was. New sensor cured it.

I'll echo what @b_r_o said about scanning it..though I'd start by looking for a pending CEL, this might be your clue.

 

Yea so it happened again tonight around 50mph it just stays around 2k revs and just seems low on power and after about 5 seconds it transitions back to normal speed super smoothly like no clunk or harsh change just instantly goes back to normal. My guess was that it was like stuck in 4th and then goes to 5th but theres no clunking or harsh shifting and I rarely notice this issue on backroads. I think I'm going to schedule an appointment at a local shop to just scan the computer. I was also curious about changing my tranny fluid which I wanted to do anyways cause I bought this used from a guy 6 years ago and have no Idea what he did or didn't do.

 

YES! That's what it feels like cause it doesnt do it in any other gear and when it does shift into 5th is smooth as butter like there is no hard shifting it just seems like it gets stuck in 4th. I think I might change the tranny fluid since that doesn't seem to expensive just to try.