Toyota: Loss of power during acceleration

I'd greatly appreciate some help with diagnosing a problem with my 94
4Runner SR5, 5 spd, 3.0 V6. I had this vehicle into the dealer I had been
going to for 8 years now, and they said "no problem found" on all my
complaints. After another dealer found the problem in my A/C, and I just
had another mechanic replace my original clutch (142,000 miles), the vehicle
still has an acceleration power loss/hesitation problem. The half decent
second
dealership said it may be related to the aging clutch, but now that it's
been replaced, the hesitation is still there. This dealership gave me an
expensive tune-up (should have seen this coming), and de-carbed the engine.
New distributor cap, rotor, wires, plugs, etc., no difference. I made them
replace the O2 sensor (I provided it), as they say they only replace them
after the check engine light comes on. Still no difference.

During acceleration, the engine seems to start pulling OK after about 3,000
RPM; I also notice sluggishness when travelling in slow conditions in 3rd
gear, where it never used to be a problem. Now I am forced to downshift.
I used to get over 18 MPG, last fill-up I got 15. Is this EGR related?
Is the catalytic converter plugged?

Any help would be greatly appreciated. It's hard to find a decent honest
mechanic, and I spend a lot of time driving this vehicle. I just want it to
be right. This is the first time it's had any problems since we bought it
new.

Thanks.

Bill
Chesapeake, VA