Need advice on next step

99 Express 3500 5.7L V-8 350

Motor rebuilt 20k miles ago, 205,000 currently
Motor ran perfect until last week. Engine started skipping, losing power, terrible fuel mileage. Also have a weird fuel smell when van runs.
I get no SES light and no code appeared when scanning.

As routine maintenance and trying to fix the problem, I replaced:
Plugs, plug wires, ignition coil, rotor button, dist. cap.
Van actually ran worse after this. My mechanic did notice 2 fouled/"fat" plugs.

I was told by another more advanced mechanic my problem is probably in the fuel meter body/"spider". Since this is a $360 part, I'm reluctant to replace it without knowing for sure?

Any thoughts?

Welcome to AF
What kind of plug fouling.
Oil or gas or coolant or just cabon?
What color was the fouling?
Does the engine have a dead miss or dead cylinder?
What kind of plugs are you feeding it?

I would be looking for a good mechanic that knows what he is doing.

Since there are no codes and it seemingly is not a basic ignition problem, consider the possibility of one of the following..
restricted cat con
restricted air intake
vac leak
bad gas
BTDT on all four at one time or another

FWIW
YMMV

Is the engine running rich or black smoke out tail pipe?
How is the fuel pressure?

Thanks for replies guys. Some of the info you want I dont know. I can get my way around a car replacing parts, but I rely on experienced mechanic friends to help me or tell me what to do.

Mechanic #1 just said fouled plug, but called it "fat"

Today I went ahead and replaced the fuel meter body. It had a SFI and the new was a MFI. From some research here, alot of people said Chevys had problems with the SFI, so I replced it since it had 205k miles on it.

Problem is still here. Mechanic #2 said it has a "dead skip" and is probably in the engine (valve ???) I cant remember his exact wording.

Since engine was replaced less than a year ago, I am going to take it back to them. Hopefully it will carry some warranty.

Good luck.
I would ask for a cylinder balance test and a compression check on it.
MT

Does the intake manifold for that engine have any kind of plug that closes off any air exchange between the two intake plenums? Have you checked that all of the intake manifold bolts are still snug? (I dont have any real knowledge, am just guessing).