GMC Repair: power and RPM loss during driving, 1995 buick riveria, fuel pressure regulator

Question
Hi there,  

     I have a 1995 Buick Riveria with a supercharged 3.8 ltr 3800 series engine and the problem is that while starting off the car has a slight shutter.  Not sure if this is the engine or transmission.  But when going about 30 mph it seems fine.  When I get to about 45 mph or higher the RPM's seem to drop off about 500 and the car shutters hard.  I have to leave off the gas pedal and give more gas to get the RPM's to go back up and get the power to go faster.  This will hold for about 3-5 seconds then drop back down.  So I have to keep pumping the gas pedal about every 3-5 seconds to keep going.  If I try and give more gas while the RPM's have already dropped the car just shutters bad.  I have to actually leave off the pedal entirely then re-apply to get this to work.  I was not sure if it was the fuel pump loosing pressure, or the fuel pressure regulator going bad, or the overdrive switch failing and engaging too early or what.  I have replaced the fuel filter and plugs and wires to no prevale.  Please help!!!!  Thanks so much.

Answer
Richard,
If it was the overdrive or the tranny. The rpm's would actually go up because it would be in a higher gear. You are definately on the right track with the fuel pump and regulator. Have you tested the fuel pressure? Test the pressure and let it sit, The pressure should drop a couple of psi after a minute or two but should then hold. Leave the tester on for about 1/2 hour and see what it is then. I take it there is no check engine light. Is the engine missing at all?
 One thing you might try is spraying wd-40 around the intake while the car is running at idle. It could be an intake leak and if it is the wd-40 will cause the engine to change the sound.Also check your injector harness connectors. Thank you for your question. I hope this helps. Jeff