3.4 Auto won’t accelerate sometimes?

Truck is a 2004 V6 Auto 4x4 Limited on 32” tires and 4.56 gears, with a transmission cooler. I’m towing a 4000lb trailer with the truck loaded; 9000lb total. Transmission drain/fill 3500 miles ago.

I’ve been towing and living on the road for about a month now and sometimes this pig just will not accelerate, other times it pulls like a freight train.

Here’s an example, all on flat straight highway: I can be cruising along (overdrive off of course) at 70-75mph at 3500-3900rpm just fine with plenty of room on the throttle, then have to slow down a bit for traffic, say to 65mph. Once I go to accelerate again, I can floor it but the truck just won’t go past 3400rpm/high-60s mph. Either I wait for a bit of downhill to gain some speed or I let off the throttle and decelerate a bunch, then punch it and get the transmission to drop a gear and spool up to 4500-5000rpm for a while to try to gain speed.

What’s going on? Am I about to kill my transmission? Probably time for a new fuel filter? I’d say the truck was overloaded and just CANT go any faster except that when it gets into that sweet spot it flys along just fine (and with the best highway mileage at the higher speed, about 10-11mpg)

Here is a video and shot of my scangauge at the time

https://imgur.com/a/uMynbD0

 

Try posting this over on the 1st Gen section.
https://www.tacomaworld.com/forums/1st-gen-tacomas-1995-2004.4/

 

What kind of trailer? I have found "utility garden" trailers with the drop gate/ramp can be a pretty effective sail, absolutely killing all gas mileage and acceleration especially on the highway when the wind is blowing the wrong way and give a nice boost if you have a tailwind.

I was having some odd bucking and acceleration issues with my old 3.4 truck after some diagnostics I replaced the throttle position sensor, cleaned the MAF, and throttle body, removed the K&N and went back tk stock, fixed vacuum leaks with a Airaid tube, and the biggest night and day improvement was rebuilt injectors flow balanced by Witch Hunter Performance.

She ran like a spanked ape after that and pulled hard. Jumped right of the line.

That said it was also a stick shift.

 

Maybe check your crankshaft sensor below the water pump. I had a leaky water pump than eventually seeped water into the connector and shorted it out. Truck wouldn't rev above 3k. Swapped out the sensor, clean and dried the wire side connection and sealed it up with dielectric grease to block future water entry.

All is good now.

 

As a follow-up for future searchers, I want to say I found nothing conclusive on this issue. I'm chalking it up as a mix of engine power, trailer weight, inclines, headwinds, and the transmission computer in disagreement on when to downshift. A 20-year-old truck can only pull so hard