Bad engine shaking when shifting from 4th to 5th

Hey guys. I've been having an issue with a pretty intense shaking coming from the front end of my truck. I have an automatic transmission btw. The shaking occurs ONLY when I accelerate slowly and when it shifts into to what i think is 5th gear. The speed this happens at is usually 35mph-40mph range, but it also will shake at 55mph-60mph range.

Ive taken it to my mechanic and so far they have checked/replaced my rear diff, driveshaft, and lastly my transmission. My mechanic even went to the extent of asking the head mechanic at my local toyota dealership and all he said was that tacoma all transmissions will eventually have this problem whether its a brand new tranny or a rebuilt one? Hard to believe that toyota would build transmissions that they knew would have issues but anyways... So after spending $3000+ on all my repairs, replacing my transmission is eventually what fixed the problem, BUT within a few weeks the shaking came back?!

My truck does have a TRD Supercharger on it, so I'm wondering that maybe it is putting too much strain on the transmission/driveline? Just throwing my problem out there to see if anyone has had the same problem as me and how they fixed it. Really do not want to have to replace my transmission again if I dont have to.

Thanks everyone.

 

My guess is it's the torque converter locking early and lugging the engine, common to some vehicles. Is the RPM really low when this is happening? Cheap easy fix might be to leave it out of OD till you're at highway speed.

 

Or the TC lockup clutch popping in and out.

Dunno about the Toyota transmissions, but on the 4L60E, the seal on the piston in the valve body starts leaking.
The TCU commands lockup. The piston leaks and it's hold weakens until it disengages. The TCU then senses the unlocked state and it re-commands lockup.
Causes a disturbing surging/shaking, and will generally disable the cruise control.

 

First off thanks for the response. Yes the rpms are really low when it happens. when i accelerate quickly the problem never occurs.

Ive been asking friends of mine that are more mechanically savvy and they have mentioned the torque converter pretty often as possibly being the problem. I will definitely ask my mechanic to have this checked out for sure. thanks again for responding.