I need help in diagnosing a problem that I'm having with a 1991 Volvo 740. It has a B230F naturally aspirated redblock engine with Bosch ignition. I recently changed the in-tank fuel pump and the fuel filter. It has good stable fuel pressure. I also changed the distributor cap, rotor, ignition wires, spark plugs, and coil. It starts and idles fine and seems to accelerate fine until I get out on the highway. Then it starts to lose power for a few seconds and then it restores power. It hesitates especially when it is under load such as going up hill. It repeats this over and over. When it is just sitting in the driveway it behaves in a similar manner. I can rev up the engine to 3000 rpms. Then (without moving my foot off the accelerator) it will go down to about 2000 rpms for a few seconds and then go up to 3000 again. It will continue to do this over and over. It doesn't throw any engine codes either. I have checked and cleaned the MAF sensor and the RPM sensor. I also checked and cleaned the connectors to all of the sensors and the ground connections on the engine and the one below the computer module on the passengers side. I'm all out of clues as far as what to check next. Do you have any leads?