Wondering if anyone can help with this.

Some background: bought this 88 F350, with 11' dump body, about a year ago from a landscaper. He replaced the original AT with a 4-speed, but I believe it's the original 351 engine.
About a month ago, the hydraulic clutch went out-- it had been slipping pretty bad and finally it caved, so I had it replaced at the local mechanic. It worked fine--no problems.
Last week, the truck just died on the way home...I had it towed to the mechanic again, and he said it was the fuel pump-- he replaced both pumps and checked the fuel filter (don't know if he replaced it).
When I picked up the truck, it started bucking about a mile from the shop-- the "check engine" light came on while this was happening like the engine wanted to die. I took it back, and he put a fuel pressure gauge on-- pressure was 35 to 40, steady at all speeds, moving or sitting. I left it to him and the next day he told me the ECM relay was bad and was sending the wrong signals to the injectors. So, I had him replace it.
It was fine for a day. Next day, I took the truck on the highway and it started to buck again, same "check engine" problem.
I notice a couple of things:
1. it happens mostly on rough road-- I was on the highway and the truck barely bucked at all on tar, but went crazy on concrete! Traveling over a DOT-roughened road also had an effect, but lesser.
2. depressing the clutch pedal makes the bucking stop, even on the concrete.
3. it doesn't miss or skip at all when the truck is still and idling.
4. it bucks more on uphill although that's not a constant thing.
5. the fuel pump "buzzes" and I told the mechanic about this, but he says this is normal. Is it? Is it related?

I'm good with the logic of truck mechanics but have no luck fixing myself, so I'm kind of at the mercy of whoever works on the truck. My mechanic is a good guy and I think he's honest.
But, he can't seem to figure it out.
Could it be a bad voltage regulator in the alternator, sending a fluctuating signal to the sensors?

Thanks for the help,
Tommy

 

I almost have to say fuel filter. I had similar problems, I think with mine.

I would be cruising along, and all of a sudden lose power and it would start acting like it was running on 5 cylinders. Absolutely no power. Stop and it would idle fine, and even rev up without a problem. Try to start from a stop and it would shudder horribly and wouldn't go.

I made it to the closest NAPA, replace the fuel filter in their parking lot and haven't had a problem since.

I checked, as in blew air through, my old fuel filter and it didn't have any restriction, but I bet there is a piece of junk in it that is getting caught and causing restriction.

If you kill the engine and let it sit for a minute, does the bucking go away, at least for awhile?

Also, my fuel pumps have always made noise and I have never had a problem. You can hear them in the cab.

 

This Site can tell you how to pull your own codes. Pull them and put those here and we can see what the computer sees.

Sorry I didn't put this in the first post but if the CEL came on, there is a code in there.

 

Hey Joe:
Thanks for the reply.
I'm glad to hear the fuel pump is normal.
The fuel filter issue sounds like it's not the same symptoms as what I'm experiencing. I had that same problem with a fuel filter on a Ford Van years ago. It just sounded awful and was just a $2.00 filter.
I'll check though.
Thanks.