93 SL1 hesitation / sluggish acceleration

[93sl1]

(This is a repost to get the proper "?" symbol. Sorry.)
I have a 93 SL1, manual, with about 65K miles.
The car has terribly sluggish acceleration, especially under load (AC on). In heavy traffic, I have to turn the AC off in order to have enough acceleration to blend into traffic. Symptoms include:
-when stepping on the gas, not much happens. Then, letting off a bit on the gas peddle causes the car to start accelerating better.
-if I step on the gas and then hold the peddle still, the car will hesitate, then accelerate some, then hesitate, and eventually it will accelerate the way you would expect.
The car seems to have power, especially when it eventually decides to accelerate, but something seems to be holding it back and not let it accelerate right away.
Very annoying when stepping on the gas while going up a steep hill, or just trying to accelerate from a stop.
The car has a new EGR valve, a new O2 sensor, new plugs and wires and filter.
Any suggestions on what to change next?
(knock sensor?, MAP sensor?, TPS?, coil?, vacuum leak?, other?)
No "Service engine" light or error codes.
Thanks for any advice.

This really sounds like a vacuum leak. What's happening(I think) as you release the gas peddle, the throttle plate is closing, and thus the amount of air going into the manifold is decreasing, thus increasing the vacuum pressure and the air velocity. When its near or at WOT, there's dead air....

On the other hand, early single cam motors don't like to have the air on while accelerating.

This is going to sound stupid, but try this: Start the engine, open the hood, and take an ordinary blow torch over to the engine. DON"T LIGHT IT! Just turn the gas on and SLOWLY move it around the engine compartment, near areas that may have a leak(manifold, hoses, etc). If the RPM suddenly rises, youve found your leak. The vacuun leak will suck in the gas and cause the RPM to increase