93 Grand Cherokee - Weird surge problem

I have a 93 grand cherokee with 200Kmiles. It idles smoothly and runs
ok but I cannot hold a steady rpm over 1000 RPM.It surges slightly
over a 300 RPM range. I've replaced cap, rotor, wires, coil, and
plugs. I've checked all the vaccum hoses for leaks. I even went as far
as to plug all the vacuun ports in the manifold and throttle body. It
still surged slightly.
I removed the throttle body and cleaned it thoroughly, replaced the
TBI gasket. I've used seafoam in the gas tank (it ran really crappy
until I filled up again). Cylinder compression is good considering
it's age (around 150psi max, 130 min).

Fuel economy is less then I expect. In a relatively hilly area I get
around 11MPG in mixed (mostly city) driving. Overall drievability is
pretty good and power is good all the way to redline. This leads me to
believe I have enough fuel pressure.

Any ideas?

Thanks in advance!

sls