Odd Shifting - Rev then Lug at slow speed

When the truck is coasting (foot off the accelerator) at a moderate speed (~20mph) and then the gas is lightly applied, the engine seems to rev up by a few hundred rpms, then drops down to around 1000rpm, and seems to lug. This is easily repeatable, and I'm considering making a recording.

Under the same conditions, when the gas is heavily applied, the truck accelerates normally.

I'm not sure if the truck is actually shifting, or attempting to shift gears, or if the few hundred rpm blip is the torque converter not actually locking up (allowing the rev), and then locking up and lugging the engine.

I've read most of the transmission TSB thread, and didn't read about this particular issue. Anybody ever experienced this? Thoughts?

 

Yeah this transmission does all kinds of weird crap. Another thing that annoys me is that if you're trying to coast at say 20 or 25 mph, take your foot off the accelerator and it seems to abruptly/prematurely downshift when you instead prefer it to stay in gear to keep coasting (like every other auto trans I've ever driven)

 

This transmission sucks, engine sucks, My truck looks nice, and drives down hills good, otherwise it's just junk. My 1991 Toyota pickup runs better than this piece of shit 2017 Tacoma off-road.

 

I would disagree with you.

I think the automatic transmission is the weak link. The engine itself has plenty of power (0-60 times are faster than previous generations), but the transmission has unfortunately been programmed to keep it OUT of its power band under anything other than WOT. This was most likely due to emission/fuel economy issues.

 

Oh boy..... try the ETC button and hit the gas.. the engine likes to be revved up some more ... sweet spot above 2500 rpms...press the pedal some more and see if that helps.

 

Most likley its not shifting. Reving up a few 100 rpm upon throttle tip in is common behavior for a lock-up clutch disengaging to help smooth the throttle transition. Then it locks back up and brings the RPM back down. This is in general, not specific to this auto....so its speculation on my part.

 

I think this is whats going on, and I probably just notice it more because of the lug afterwards (because transmission keeps RPM so low).

 

This is an issue of much debate whether or not the source of low end torque is a powerplant issue, a software (shift mapping) or a drivetrain issue. Either way it leaves a lot to be desired for a truck. And before someone says "if you wanted a fast vehicle you should have bought a car"---- it isn't about speed, it is about the lack of low end torque, delayed throttle response and sketchy shifting.

 

Under light throttle, the transmission will aggressively upshift to keep the RPM low and maximize MPGs, but if the throttle is applied heavily, then it will hold the gear it's in for a longer time and allow the RPM to increase.
Each test cycle for the EPA's MPG test has a maximum acceleration component. I'm sure the transmission computer knows these limits and uses them to maximize MPGs, but the effect is the transmission aggressively upshifts to higher gears than it would traditionally and puts you in lower RPM, which lack any power.

https://www.fueleconomy.gov/feg/fe_test_schedules.shtml