Volvo: 1990 VOLVO 740- SENSOR???HELP!!!, grasping at straws, volvo 740

Question
Hi,I am at my wits end with my 1990 Volvo 740 station wagon.Lately it has stranded me twice on the highway late at night because it will be going along just fine but then it decides it wants to lose power and almost die out and then I can put the pedal all the way to the floor but it won't go any faster than 5 km's an hour!Then it will surge and sputter and when I pull to the side of the road and shut it off it sputters and I hear a whirring noise coming from the back of the vehicle which I believe is the brand new fuel pump I had installed just last year.It seems that after I let it sit for at least 15 minutes it will go again but then it will only last a minute and will do it all over again.I had it into a garage and they had it there for a week and installed all new plugs and wires and new fuel line which had been leaking quite badly.They could not get into my computer to do a diagnostic and after almost $800 later the car still acts the same.They even tried putting something in the gas tank incase it had moisture in it that was making it sputter.The check engine light comes on every now and then but not always.It has also just had a brand new oil and filter change,they used 5w30 I always used 10w but I'm sure that wouldn't have anything to do with it. I think I have a bum sensor ,but I really have no idea as to what could be the matter. Could it be a plugged fuel injector? I am just grasping at straws here,you are the expert Jason, Please HELP me!Thanks in advance.

Answer
Ok, before I say anything I have to admit this is about the toughest question to answer, not being able to drive your car.  I would assume a bum sensor first, but without having a computer diagnostic ran, there's no telling which one.  It was a 'cam positioning sensor' on my friend's car that caused similar symptoms, but again, computers.  5w30 is just a lighter oil that would thin quicker at high temperatures...since summer's coming, I would suggest returning to 10.  But I don't think that would have an affect on your problem.  I would definately check you fuel injectors for clogs.  I think you're probably right in assuming a sensor, though, since it's as intermitten as you say.  If you manage to get this resolved, please fill me in!
JD