In my opinion, definitely not the fuel pump relay. This relay will only stop the fuel pump from running if it fails. When off the throttle and above around 1500rpm, no fuel is delivered to the engine anyway (no point if engine is not being needed to produce power), the engine is just turned round by the turning of the wheels. So if you are experiencing problems in these conditions, it's unlikely to be fuel-pressure related.
The fuel pump relays *can* fail in these (mine did), and the symptoms were, sometimes the fuel pump would not run when you switched the ignition on (should buzz from rear for 1-2 seconds, and continually when running), and the result was the car had no fuel pressure and wouldn't start. New relay = £75, I just opened mine and soldered a broken joint. No problems since.
The relay never suddenly switched the pump off while driving in my case, and would be unlikely to cause the jerking you described.
Is/was the car fine when 'on' the gas?
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black