Cadillac Repair: 89 Brougham, car coast, torque converter

Question
I own an 89 Brougham with a carbureted olds 307. I have recently been experiencing a strange problem with the engine. Whenever I am driving on the highway and trying to maintain a certain speed, say 60, the engine will suddenly rev, the check engine light will come on, and the car will slow down. The light will stay on unless I take my foot off of the throttle and let the car coast for a few minutes. If I flutter the gas, then this problem does not occur.

I have gotten several opinions on what this problem could be. One guy said it is the carburetor, another said it’s a clogged fuel filter. The last guy I talked to said that the transmission torque converter is causing it.

What I can tell you is that the engine has a Motorcraft carb (in place of the Rochester). The fuel filter has not been replaced in the two years since I have had the car. And the car will not move for a few seconds after I shift into reverse (basically the tranny needs to be rebuilt).

Could you give me one last opinion? All of the above will be taken care of, but I would like to find and fix this problem first.  

Answer
Sven,
Based purely on your description, my guess would be transmission problem. The only thing that would cause the engine to suddenly rev while running at a steady state is a sudden removal of load. The only thing I can think of that could accomplish that is the transmission suddenly slipping.
You say the check engine light comes on. Have you retrieved any codes from the ECM yet? This would most likely point to a cause of the problem.