My brain hurts!

My 93 Trooper has acquired a habit of chugging below 3000rpm after about 2 min of running from a cold start. I racked my brain, swapped sensors, checked the timing, cleaned the EGR tube and valve, changed all the vacuum lines, tried high octane fuel for a couple tanks, and ran seafoam through a tank of fuel. All as I was able to over the last 6 months or so.

Last fall it was acting similar but since I was working I took it to the Saturn/Saab dealership since they used to be the local Isuzu dealership to get looked at. they discovered that the fuel pump was only producing about 8psi, and the filter needed to be changed. $1200 later she ran like a dream, for a month then slowly started developing the current problem.

For two or so min after I start it from sitting over night it runs like a dream with tons of power. After that getting moving in first is a bit of a feather the gas and clutch job. Once I get up over about 2500rpm or so it takes off with tons of power again.

Occasionally when I let off the gas the rpm will drop to about 200 and sputter and cough for a few seconds before rising back to 750 or dying.

In the last week it has developed another symptom, black fuel filled exhaust for the first little bit after I start it, which goes away as the converter warms up..

One thing that I haven't done yet is to hook up a vacuum gauge in the cab to monitor the vacuum while driving. I don't have a vacuum gauge to do this at this time either.

The CE light hasn't come on, it didn't come on when the fuel pump wasn't working either though.

I need some help with this, any and all suggestions would be greatly appreciated. Thanks so much.