Intermittent Hesitation; confused

95 5-speed 4WD 2.7l Tacoma 193k, well maintained with a recently rebuilt top-end (new head) lots of new parts due to maintenance. Runs great.

• New clutch at 170k (hardly worn when replaced)
  
• New Front wheel bearings, new stock suspension and steering rack.
  
• All new brakes
  
• Head replaced with new due to cracked head secondary to a clogged thermostat (antifreeze mixture incompatibility)
  
• New stock-type header, new OEM catalytic converter, new O2 sensors, Flo-pro max muffler; no leaks
  
• New distributor cap, rotor, wires and iridium plugs (for longevity) gapped to 0.30.
  
• K&N filter (stock type)
  
• Recent fuel filter changed
  
• Lots of other new parts
  
• "New" as in the last 20k miles

I will be driving down the road in 5th gear when my truck suddenly loses power. This is not because I suddenly let my foot off the pedal and then tried to speed up without downshifting.

What's weird is that I will downshift into fourth gear to try to pick up speed, but 4th also has a difficult time. It's like a cylinder shut down. It shudders and feels exactly like the clutch is slipping. I have to slow down and shift into third and get most of my speed from it before shifting back into 4th, then 5th.

The terrain that makes this happen is normally flat with some rolling hills.


I was thinking that it could be the transmission or the clutch getting hot.

Or it could be a bad bearing somewhere?


Or maybe my fuel injectors are clogged. I noticed that the intake was pretty dirty. I managed to clean what I could, but I have not attempted to clean the throttle body yet.

Build-up of carbon during cruise?

My emmisions report came out ultra low, lower than most trucks on the road. They were impressed.

I am lost.... Any help would be appreciated.