running problem under load

OK, This is tricky.

My friend has a 96 Tacoma with a 3.4, 5 speed, 2 wheel drive (not pre-runner) Anyways, it started running really rough under loads. Such as starting out and on hills. It was a jerking kinda ride. He took it to Big O tires as it was the closest place that all this stuff started happening. They did a real quick check of the truck and said that the engine was 100% running fine and that they felt it was the clutch.

He the took it to a transmission shop that was recommended by them. They didn't even test the truck and quoted him $650 dollars to replace it. He then told me that he needed a clutch and was quoted $650 to have it done. I told him I would do it for him for the cost of parts. I ordered the parts and when they came in I called him to bring the truck over so I could get started.

I then tested out the truck before doing any work to see for myself what it was doing. It wasn't slipping at all and was shifting pretty well. I told him I didn't think it needed a clutch at all. He wanted me to install the clutch anyways as the parts were all purchased and couldn't be returned.

Now the truck shifts really well but the rough running is still there. I wasn't sure what it could be so he took it back to Big O. They then said it ha missfire code come up in the computer and it needed a full tune up and they replaced the fuel filter. We then bought plugs and wires, PCV valve and replaced the air filter. We also put in a fuel injector cleaner. The truck is still running rough under load. As soon as you push the clutch in it runs smooth and revs smooth. Going up this long hill the truck will only hit 55mph when it used to pull all the way up it at 75 with no problems.

What else could be the problem? Any ideas?

Thanks in advance.

 

Take it to the dealer, not "Big O". I would also get a Scangauge so he can see what codes the computer is throwing on his own.