My troubles began when my 2.3L would cough, backfire, and lose power at higher rpms. The local mechanic diagnosed the problem as a bad Mass Airflow Sensor and the truck ran fine for a few weeks.
As soon as I noticed the symtoms returning, I went back to the mechanic, and he changed the MAF sensor again(no charge). He also installed new plugs/wires.
The truck ran fine at idle to 1/2 throttle, but puttered and misfired over 1/2 throttle.
Then the mechanic changed the fuel filter, and blew out the lines. This worked for about a week. He now said there was water in my fuel and flushed out the tank, and I changed the filler hose as there was a hole in it.
The truck now usually runs OK for a few minutes, but then will begin to putter like a VW bug and run poorly. It smells funny too. Sometimes the problem will intermitently come and go.
The mechanic has refunded most of my money, said he has tried numerous MAF sensors, tested new coil packs, and said " all the sensors are new ".
He gives up.

 

How's the cat converter working? Is it working?

No codes? Well, the converter won't necessarily set off a code and when mine went bad, it ran fine but smelled NASTY RICH! Yours could be clogged, which would explain the loss of revability...and the smell

Also, check for vacuum leaks, TB unit, hoses, etc.....

Check the timing, too. It should be okay, but do so if you sense the belt jumped a tooth.

If I guessed right, tip the mechanic real good and maybe he's worth keeping for giving a refund like that! Most would back off and rip you a new one to boot!